HPLS DOI 10.1007/s40656-014-0052-8 ORIGINAL PAPER
Folding into being: early embryology and the epistemology of rhythm Janina Wellmann
Received: 8 July 2014 / Accepted: 16 November 2014 Springer International Publishing AG 2014
Abstract Historians have often described embryology and concepts of development in the period around 1800 in terms of ‘‘temporalization’’ or ‘‘dynamization’’. This paper, in contrast, argues that a central epistemological category in the period was ‘‘rhythm’’, which played a major role in the establishment of the emerging discipline of biology. I show that Caspar Friedrich Wolff’s epigenetic theory of development was based on a rhythmical notion, namely the hypothesis that organic development occurs as a series of ordered rhythmical repetitions and variations. Presenting Christian Heinrich Pander’s and Karl Ernst von Baer’s theory of germ layers, I argue that Pander and Baer regarded folding as an organizing principle of ontogenesis, and that the principle’s explanatory power stems from their understanding of folding as a rhythmical figuration. In a brief discussion of the notion of rhythm in contemporary music theory, I identify an underlying physiological epistemology in the new musical concept of rhythm around 1800. The paper closes with a more general discussion of the relationship between the rhythmic episteme, conceptions of life, and aesthetic theory at the end of the eighteenth century. Keywords
Rhythm Rhythmic episteme Embryology Development Folding
1 Introduction In the history of biology, the time around 1800 is usually considered as marking the beginning of the modern life sciences, highlighted by the move from a preformationist theory of generation to the new theory of epigenesis focusing on J. Wellmann (&) Leuphana Universita¨t Lu¨neburg, MECS – Medienkulturen der Computersimulation, Wallstraße 3, 21335 Lu¨neburg, Germany e-mail: [email protected]
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the process of the gradual development of the embryo. Pivotal to this story is the work of the German Caspar Friedrich Wolff, notably his epoch-making work Theoria generationis of 1759. The significance of this work for the history of embryology can hardly be overrated. In it, Wolff endeavoured to do nothing less than conceive a new theory of organic development, which went far beyond contemporary views pro and contra epigenesis or preformation. Following Wolff, at the beginning of the nineteenth century Christian Heinrich Pander and Karl Ernst von Baer developed the theory of germ layers—until today the basis of modern embryology.1 By the third decade of the nineteenth century, the foundations of modern embryology, as the science of development, had largely been laid. But what is development? How was development envisaged by Wolff, Pander and Baer, and what was new in their approach? Merely to say that their views were ‘‘epigenetic’’ hardly helps understand the underlying epistemology of their work. For example: What was behind Wolff’s claim that the embryo only gradually forms from an originally homogeneous mass? Why did Pander and Baer decide to trace all development back to the formation of four germ layers? And most importantly: What was development for them? How did they investigate it, observe it, represent it? Historiography has customarily regarded the emergence of the epigenetic theory of development and embryology around 1800 as a part of a new world view often described as ‘‘temporalization’’ or ‘‘dynamization’’. The end of the ‘‘representation’’ of the classical episteme as a ‘‘form of simultaneity’’—as Michel Foucault put it in The Order of Things (Foucault 1974, 337)—marked a breach in the entire order of knowledge towards the end of the eighteenth century. From then on, ‘‘a profound mass of time’’ was precipitated into the ‘‘old flat world of animals and plants, engraved in black on white’’ (Foucault 1974, p. 138). Largely following Foucault, Wolf Lepenies in his Ende der Naturgeschichte formulated the adage of the ‘‘empirical imperative’’ resulting from the ‘‘pressure of experience and observation.’’ According to this thesis, the temporalization of nature became inevitable as soon as the mass of the new knowledge threatened to burst the horizontal level of space (Lepenies 1976, p. 18; see also Lovejoy 1936; Koselleck 1975; von Engelhardt 1979; Richards 2002; Stockhorst 2006). But is ‘‘temporalization’’ a sufficient answer to the question of how development was understood around 1800? Mere progress in time does not seem to be an adequate explanation for the new understanding of biological development in this period. Obviously, organisms were considered to have a temporal dimension long before 1800. Even the theories of preformation had by no means denied progressive change. In fact, the new questions that were asked in the late eighteenth century went far beyond the temporalization of biological processes; they touched upon the underlying dynamics of the temporal. When scientists of that period gazed through the microscope, observed hens’ eggs and dissected organisms, prepared them and compared them with one another, they increasingly realized (and tried to capture) the ambiguous nature of the living world: on the one hand well-ordered, a 1
On the history of embryology, see; Needham (1959), Adelmann (1966), Gasking (1967), Roger (1963), Roe (1981), Gilbert (1991), Oppenheimer (1967), Smith (2006).
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functioning realm, on the other permanently changing, in transition, every form simultaneously structure and the disintegration of that structure. In particular, they asked how the nascent organism developed into a highly complex structure while its parts and its whole changed uninterruptedly. This paper posits that the episteme of rhythm provided an answer to these questions. Unique and essentially new in the conceptualization of development around 1800 was its underlying rhythmical epistemology. Rhythm may be a temporal structure, but unlike the continuous flux of time, it implies the restriction of the flux in favour of a rule.2 Indeed, it was this very feature that explained the power of rhythm around 1800: rhythm’s ability to structure temporal processes. Rhythm did not suspend time, but subjugated it. It subjected to a rule the incessant change to which organic becoming was exposed. Thus, around 1800 nature was not merely conceptualized as temporal and changeable. In fact the contrary was the case: rhythm was considered to be the law under which nature’s temporal dimension could be unfolded. Hence establishing a science of becoming did not imply imagining the organism as an essentially dynamic and temporal entity, but as a being whose most important manifestation is order under the condition of temporality. Rhythm thus described the generation and formation of what is living as an order of time. This paper argues for the central role of the rhythmical episteme in the establishment of the science of embryology around 1800. In the first section, I show how Caspar Friedrich Wolff’s epigenetic theory of development was based on a rhythmical conception, namely the hypothesis that organic development occurred as a series of ordered rhythmical repetitions and variations. The second section is devoted to Pander’s and Baer’s theory of germ layers. Central to this theory is the idea that the entire development of the embryo occurs as a gradual differentiation of primary germ layers. One central aspect of Pander’s and Baer’s work, an aspect that has hitherto almost entirely escaped the attention of scientists and historians, is the principle of the fold.3 As I will show, Pander and Baer made folding an organizing principle of ontogenesis: all the changes in the egg during early embryonic development, in their view, take place as a series of foldings of the germ layers. The explanatory power of this scheme, I maintain, stems from the understanding of folding as a rhythmical figuration. In my discussion of the embryological investigations of Wolff, Pander and Baer, I use the concept of rhythm mainly as an analytical category. More generally, though, I argue that the concept of biological development after 1800 (and essentially up to the present day) is fundamentally rhythmical. However, my 2 Usually, the Greek word rhythmos is considered to derive from the root rhe´ein, ‘‘flow,’’ ‘‘protect,’’ but alternative derivations have also traced the concept to ‘‘draw’’ or ‘‘fend off’’ as well as ‘‘protect.’’ In his seminal study, Emile Benveniste substantiated the etymological proximity of the concept of rhythm to the meanings ‘‘shape’’ and ‘‘form’’ or ‘‘figure.’’ Benveniste speaks of rhythm as the ‘‘shape of the fleeting and changeable’’ or the ‘‘order of time’’ (Benveniste 1966, I, 326–335); for the etymology, see also (Trier 1949; Seidel 1976, 15; Seidel 2003). 3
Whereas the history of biology has consistently acknowledged Pander and Baer as the authors of the theory of germ layers, this aspect of their work has gone practically unnoticed (see, for example, Churchill 1991; Oppenheimer 1963; Raikov 1968, 1984; Brauckmann 2011). Schmitt calls the concept of the fold an ‘‘avance´e conceptuelle considerable,’’ but does not go into detail (Schmitt 2003, 161).
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argument is also a more specific historical one. I maintain that it was not a coincidence that biologists around 1800 attempted to understand the living world in rhythmical terms. In fact, around 1800 the idea of rhythm and especially the claim that life is essentially rhythmic can be found not only in embryology, but also in many other fields of knowledge. The idea of a rhythmically organized nature was based on an episteme of rhythm that was simultaneously the basis of new aesthetic concepts in the era’s poetology and music theory as well as expressing itself in other scientific theories. This is the subject of the third part of this paper. There I briefly discuss the notion of rhythm in contemporary music theory and stress the physiological epistemology of the new musical concept of rhythm. Finally, I touch upon the more general aspect of aesthetic theories around 1800 by discussing the work of Karl Philipp Moritz, who formulated one of the most influential aesthetic concepts of the time, notably his notion of ‘‘aesthetic autonomy.’’4
2 Repetition, pulse, spiral Most accounts of Caspar Friedrich Wolff’s theory of generation focus on his early writings, notably his doctoral thesis of 1759 (Wolff 1896), and tend to place his work in the context of the debate on epigenesis versus preformation (Schuster 1936; Uschmann 1955; Herrlinger 1959; Jahn 1998/1999; Mocek 1995; Witt 2008). However, if we widen the perspective to include Wolff’s later work, and attempt a more careful reading of his embryological observations, a new understanding of his epistemology emerges. In particular, I argue that Wolff conceived of the genesis and development of the embryo as the interplay between three moments: repetition, pulsation, and spiral motion. De facto they are linked, and as a unity form the complex structure of Wolff’s rhythmical episteme of epigenesis. In Wolff’s work, we find the episteme of rhythm framed as a continuous movement or flow, which at the same time is an ordered and controlled movement composed of several components or sub-movements. It is the ability to structure the flow in various ways by alternating the order of the sub-movements which stands at the heart of Wolff’s epigenetic imagery. The rhythmic variation is based on three elements: repetition, pulsation and spirality. Wolff’s point of departure is the search for a universal principle of all processes of organic formation (Bildung). Wolff assumes that such a principle should underlie not only embryogenesis but practically all physiological processes. Nutrition, growth or reproduction are therefore not distinct physiological events, but merely variations of the same underlying theme. The vital processes of the organism are to be regarded as one and the same basic constellation that is constantly repeated, but varied in the repetition—for example when the processes take place temporally or geographically offset, in isolation or continuously. Only the specific 4
My book, Die Form des Werdens. Eine Kulturgeschichte der Embryologie, 1760–1830 (Wellmann 2010), presents in more detail the simultaneous emergence of a new treatment of the organic in several different disciplines such as music theory, poetology, philosophy, aesthetics, embryology, physiology and botany.
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circumstances ‘‘accompanying this process’’ (Wolff 1896, I, Sect. 25, p. 8) determine whether a process is called nutrition, growth or reproduction.5 Secondly, epigenetic development is pulse, pulsating—the continuous alternation between two states. Here my reading of Wolff’s work significantly differs from that of existing scholarship. It is commonly claimed that the central features of Wolff’s epigenesis were his emphasis on the homogeneous and amorphous beginning of development, and the gradual emergence of structures out of this state. In addition, Wolff is said to have postulated a force guiding this development—the ‘‘essential force’’ or vis essentialis (see Witt 2008, p. 650; Roe 1981, p. 103; Oppenheimer 1967, p. 141; Gasking 1967, pp. 97–106; Detlefsen 2006). However, no attention has been paid to how Wolff viewed the interaction between force and matter, which I argue was as a rhythmical dynamic of flow and standstill. At the very beginning of his thesis, Wolff introduces this elementary idea, on which all his further considerations on development are based: he traces all vital processes back to the same basic movement, the constant interaction between the flowing and solidification of plant and animal fluids. Nutrition, growth and development can all be reduced to the oscillation of nutritive fluid (Na¨hrsaft) between movement and standstill. Wolff underlines the fundamental claim of this approach in two ways: not only can all vital processes be traced back to this movement, but—and this generalization is essential for Wolff’s approach—it applies both to plants, discussed in the first part of the dissertation, as well as animals, which Wolff treats in the second part. For Wolff, the mutually conditioning interaction of the movement and stasis of organic fluids is a sufficient grounding for the formation of any structure in the organism. Thus, flowing alone does not explain how the nutritive fluids coagulate and the formation of structures comes about. Interruptions and breaks are also necessary, as ‘‘only as a result of stasis does the fluid [Flu¨ssigkeit] begin to thicken and gradually deposit solid parts’’ (Wolff 1896, I, Sect. 35, p. 23). The break in the flow, the pause, the interruption of the flux is the real moment of development, for ‘‘in a state of standstill the nutritive fluid can easily deposit something of its mucous substances [schleimige Stoffe] … in vesicles [Bla¨schen] here and there’’ (Wolff 1896, I, Sect. 36, p. 23). Wolff goes a step further by qualifying the movement of the nutritive fluid more precisely: the rhythm of the fluid’s movement determines the specific form of the structures formed. The very first structures that can be identified in the liquid are vesicles and vessels. Fluids in motion form vessels. These, in turn, when they come to a standstill and are deposited, are responsible for the formation of vesicles (Wolff 1896, I, Sect. 41, p. 27, Sect. 23, p. 18, Sect. 28, p. 20). In addition, a slow flow produces ‘‘regular’’ structures, whereas the alternation between stagnation and flow generates ‘‘irregular cell membranes’’ (Wolff 1896, I, Sect. 35, p. 23). The third element in Wolff’s concept of rhythmical development is that of the spiral, that is, variation within repetition. Wolff’s notion of spiral development, as ¨ ber die Bildung des Darmkanals im bebru¨teten elaborated mainly in his work U Hu¨hnchen of 1768 (Wolff 1812), would become tremendously influential on the 5
Here and throughout, all translations are my own unless stated otherwise.
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development of embryology, notably on the work of Christian Pander and Karl Ernst von Baer (discussed below).6 The basic tenet of Wolff’s 1768 work is that organs do not develop independently of each other, but always as parts of whole organ systems. Moreover, all organ systems are formed in the same way, namely by membrane folds. Each and every developmental path is nothing but a series of repeating folds. The peculiar series of foldings at different points of time bring about a gradual differentiation into specific organs. Wolff observed that initially the two surrounding membranes bend and fold, grow together at the edges and form the three sections of the intestinal system, as a result of this movement and contraction (Wolff 1812, pp. 132–133). However, these forms do not lead directly to the intestinal tract in its final form. On the contrary, Wolff observed that the existing forms were replaced by completely new structures after the end of the fifth day, triggered off by a new sequence of folds (Wolff 1812, pp. 183–184, 187). Through a series of meticulous observations, Wolff showed how the intestinal tract is practically formed and deformed, structured and restructured several times by the repeated formation and disintegration of different membranes. In other words, embryogenesis is not a simple linear generative process, but a back and forth of construction and destruction of forms through repeated folding. With the elements briefly sketched here, Wolff set embryology on completely new foundations. His approach was based on tracing development back to the elementary phenomenon of movement. The specific qualities of organic development result from the rhythmical, pulsating constellation of movement and stasis, repetition and variation, stability and change.
3 Membranes, tubes and foldings The physiology of the eighteenth and the early nineteenth centuries described the basic substance of the organic as ‘‘mucous’’ and amorphous on the one hand, and on the other as manifesting some kind of basic structure—descriptions varied, and included ‘‘grains’’ and ‘‘corpuscles,’’ ‘‘vesicles,’’ ‘‘globules’’ or ‘‘cellular tissue’’ (Do¨llinger 1821).7 The detection of the stages of development from the seemingly unstructured fertilized chicken egg to a fully developed embryo stood at the centre of the groundbreaking work Beitra¨ge zur Entwickelungsgeschichte des Hu¨hnchens im Eye published by Christian Heinrich Pander in 1817 (Pander 1817). Working under the guidance of the Wu¨rzburg physiologist Ignaz Do¨llinger, the young Pander gave special attention to the transition from freely moving ‘‘granules’’ or ‘‘corpuscles’’ (Ko¨rnchen) to structured layers or membranes. The importance of this step, the conceptualization of embryogenesis in terms of layers and membranes, can hardly be overestimated. It gave embryology a new 6
Wolff’s doctoral thesis Theoria generationis aimed to provide a theory of the development of basic organized structures from homogeneous, amorphous matter. In his later work on the genesis of the intestinal tract (De formation intestinorum, written in Latin in 1768 and published in a German translation by Johann Friedrich Meckel in 1812), Wolff went one step further and focused on one organ to trace the formation of complex organic structures from already existing, simple formations.
7
Not to be confused with ‘‘cells,’’ discovered only in the late 1830s.
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conceptual and visual language that by and large still underlies the science 200 years later. As I will argue in the following, Pander’s ability to describe development in terms of the folding of membranes relied heavily on an underlying rhythmic epistemology. In order to grasp this epistemology, I analyse in some detail key passages from Pander’s (1817) publication. 3.1 From corpuscles to layers Pander’s point of departure is the non-incubated fertilized egg, in which he describes the germ layer as initially consisting ‘‘of a simple layer made of interconnected corpuscles’’ (Pander 1817, p. 5). After 12 h they have formed two layers, slightly detached, enough so for Pander to discern two distinct layers—he calls them the serous layer (sero¨ses Blatt) and the mucous layer (Schleimblatt). They are distinguished by the different structures of the vesicles from which they were formed—a coarse grainy structure on the inside and a more homogeneous form on the outside (Pander 1817, pp. 6–7). After about 20 h of incubation, a further metamorphosis of the germ layer commences, leading to the formation of a third layer between the two already existing ones: the vascular layer (Gefa¨ßhaut). This layer also arose in the formation of the grainy mass of organic material (Pander 1817, pp. 13–14). Thus after 24 h the germ layer consists of three membranes, forming the basis for the emergence of all other forms in the egg. Everything that now happens in the egg must be seen as ‘‘never for anything else but a metamorphosis of this membrane and its layers [Bla¨tter], endowed with the inexhaustible abundance of the formative drive [Bildungstrieb]’’ (Pander 1817, p. 6). 3.2 From layers to folds From this point on, Pander makes the spatial shifts of the germ layers the organizing principle of the formation of new structures in the fertilized egg. In particular, he aspires to understand the underlying logic of the movements of these membranes, their warps, their changes, their gradual moving towards and away from each other, or their coalescence into one membrane. All these processes, Pander believes, can be understood in terms of a single dynamic, namely that of folding.8 Pander distinguished three kinds of folds. The first fold takes place in the mucous and the serous layers, which begin to fold after 18 h of incubation. This first fold produces the primitive streak with its two primitive lateral folds (Primitivfalten). They mark the beginning of the embryo. In the germinal area (Keimhof), the 8
The germ layer ‘‘itself forms the body and the intestines [Eingeweide] of the animal solely through the simple mechanism of folding. A tender thread attaches itself as a spinal cord, and no sooner has this happened than it forms the first folds, which even have to show the spinal cord its location, as a cover over the precious thread, this way forming the first basis for the body. Then it makes a new fold, which, unlike the first, fills the abdominal and thoratic cavities [Bauch- und Brustho¨hle] with content. And it sends out folds for the third time to wrap the foetus formed from it and by it in suitable envelopes [Hu¨llen]. So nobody should be amazed if there is so much talk of folds and changes in the course of our narration’’ (Pander 1817, 7).
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primitive streak initially develops as parallel folds, which then unite in an arch at the top end and remain open at the bottom (Pander 1817, p. 8). The future head of the embryo is produced at the closed end of the fold. Subsequently, the primitive folds envelop the beginnings of the spinal cord by turning over at their joint end (Pander 1817, pp. 9–10).9 Underlying this succinct description was a highly complicated process of folding, the explanation of which posed one of the greatest challenges in Pander’s investigation. Essentially, Pander describes the process in the following way: the approach and unification of the primitive folds does not occur abruptly; first, ‘‘the primitive folds are bent in waves along their entire length.’’ Then ‘‘the edges of these folds join’’ in the middle and ‘‘by growing together’’ they form ‘‘a seam that covers the part of the spinal cord below it as a whitish strip.’’ At a later moment, ‘‘the two folds join at the top and bottom.’’ At the lower end, the folds separate at ‘‘an acute angle’’ with the spinal cord visible between them. At the top end, they run in parallel but separately from each other as far as the sickle-shaped fold, then ‘‘they curve like waves,’’ but their edges remain standing ‘‘straight up.’’ In this way, ‘‘spaces or cells’’ develop, increasing in size towards the head region (Pander 1817, p. 10).10 A second folding, this time of the primitive streak, produces two further structures that will later give rise to the oesophagus and the heart. It is important to note that every movement by one of the membranes also affects the others. Therefore, folding takes place on several axes, horizontally and vertically. As the lateral folds continue to approach each other, finally to meet in the middle, there emerges a ‘‘space formed by the descending part of the layer and separated into two pipe-shaped tubes.’’ Of these, each forms a ‘‘sac closed from the top and the sides and open towards the bottom’’ (Pander 1817, p. 12). The first sac marks the origins of the oesophagus and the second those of the heart (Pander 1817, pp. 12–13). In a further metamorphosis, the tube of the heart formed by the folding of the membrane finally changes ‘‘into the completely formed heart’’ through additional ‘‘folding, sometimes binding [Verschnu¨rung], contraction and expansion of its walls’’ (Pander 1817, p. 18).11 9
What Pander observed here (and Baer later realized) was the notochord.
10
‘‘Allein dieses Anna¨hern und die Vereinigung derselben [der Primitivfalten] geschieht nicht auf einmal, so dass sich das Ru¨ckenmark plo¨tzlich unter diese Hu¨lle versteckte; sondern erst werden die Primitivfalten in ihrer ganzen La¨nge wellenfo¨rmig gebogen, und zwar so, dass jede Erweiterung dem Zwischenraume eines jeden Wirbelrudimentes entspricht, und jede Verengerung dem anliegenden, rundlich-viereckigen Ko¨rperchen desselben. Dann legen sich in der Mitte die Ra¨nder dieser Falten an einander, und bilden durch ihr Zusammenwachsen eine Naht, welche als weisslicher Streifen den unter ihr liegenden Theil des Ru¨ckenmarkes bedeckt. Nicht so schnell vereinigen sich die beiden Falten oben und unten; nach unten gehen sie unter einem spitzen Winkel aus einander, und zwischen ihnen zeigt sich alsdann unmittelbar der Faden des Ru¨ckenmarkes mit seiner lanzettfo¨rmigen Endigung; nach oben weichen sie auch unter einem scharfen Winkel von einander ab, laufen aber, bis zum sichelfo¨rmigen Umschlage getrennt, neben einander, kru¨mmen sich wellenfo¨rmig, und indem ihre Ra¨nder nicht eingeschlagen, sondern gerade in die Ho¨he gerichtet sind, entsteht zwischen ihnen eine Reihe von drei bis vier gegen das Kopf-Ende an Gro¨sse zunehmenden Ra¨umen oder Zellen, anscheinend auf jeder Seite von zwei Linien eingefasst, weil die beiden Bla¨tter, woraus jede Falte besteht, als Linien durch ihren Rand durchschimmern‘‘(ibid., 10). 11
For details, Pander refers to work by Haller and the drawings of Malpighi (see Haller 1758; Adelmann 1966).
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Whereas the second folding is taking place in the head region of the primitive streak, the third happens at the bottom or tail end. A few hours after the second folding, a ‘‘similar folding, but different in size and form’’ occurs at the tail end of the foetus (Pander 1817, p. 21 also pp. 23–4). The third folding is ‘‘very similar to the two preceding ones … but now the entire development is turned to the outside and proceeds over the embryo’s back,’’ whereas the two foldings already described ‘‘formed at its ventral side and the folds were turned towards the yolk’’ (Pander 1817, p. 24). The three foldings are similar, in that initially all three layers mutually affect each other ‘‘until the serous layer reaches a stage in which it is able to lead the process on its own’’ (ibid.). The third folding, thus, takes place at the bottom rather than the top end of the primitive streak; it happens at the dorsal rather than the ventral side of the embryo; and it folds to the outside rather than to the inside. Because the folding starts in a different section of the membrane and takes a different direction, what is produced are not the tubular beginnings of the inner organs but the extra-embryonic membranes, in this case the amnion. The two lateral folds gradually grow together along a back-seam (Ru¨ckennaht) from the head to the tail end of the embryo. This produces two cavities. The first Pander calls the ‘‘true amnion,’’ which resembles ‘‘a sac filled with water’’ or a ‘‘bladder’’ (Blase) of the inner layer, which wraps up the foetus ‘‘down to its abdomen.’’ The second is the ‘‘false amnion,’’ formed from the outer layer (ibid.). The false amnion, which can hardly be discerned as an autonomous membrane, replaces the vitelline membrane (Dotterhaut). Another extra-embryonic membrane, the chorion, is similarly produced at the lower end of the foetus —but this only happens once the amnion has reached completion and the intestinal tract has developed enough for the oesophagus and the rectum to be differentiated (Pander 1817, p. 25). By describing the formation of the primitive streak, the intestinal tract, the heart, and the thin layers surrounding the embryo, the amnion and the chorion, Pander provides a comprehensive explanation of the formation of the elementary organ systems in early embryogenesis. His view of this development is based on three rhythmical foldings of the membranes, recurring periodically and repeating themselves at different locations of the developing egg. The foldings are very similar and yet not identical—like rhythmical waves that produce the forms of the future living creature with their movement. 3.3 From layers to tubes ¨ ber Entwickelungsgeschichte der Thiere. Beobachtung und In the first volume of U Reflexion, published in 1828 (Baer 1967), Karl Ernst von Baer described in much greater detail the process of folding that Wolff had imagined and Pander had sketched. For Baer, too, the germ layers were at the centre of his observations and his concept of differentiation. However, Baer considered the movements of the membranes to be so complex that he accepted Pander’s concept of the fold only with reservations. The process could only be presented ‘‘as a fold in a schematic drawing,’’ he wrote in the 1860s (Baer 1972, p. 298). As I argue in the following, Baer did not reject Pander’s fold but expanded it. While Pander imagined it essentially in two dimensions, as a kind of line, Baer imagined a surface or plane
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that is extending, moving, bending, curving and shifting in all three dimensions of space, and also changing shape even on isolated spots of its surface through the accumulation of organic substance. For Baer, formation takes place through a process of segregation or separation (Sonderung), a process that today might refer to a series of differentiations and the formation of specific organs (organogenesis). In particular, Baer distinguishes three kinds of ‘‘Sonderungen’’: (a) the ‘‘primary differentiation’’ or the differentiation into four germ layers, (b) the ‘‘morphological differentiation’’ into primitive organs, and (c) the ‘‘histological differentiation’’ within these layers. Like Pander before him, Baer describes the ‘‘formative tissue’’ (Bildungsgewebe) or the ‘‘basal substance of all animal parts’’ (Grundmasse aller thierischen Theile) as ‘‘albumen-like primitive mucous’’ (eiweissa¨hnliche Grundschleime) consisting of ‘‘partially separated corpuscles,’’ in other words accumulations of corpuscles distributed irregularly in the basal substance (Baer 1967, I, p. 19). Development now commenced with the differentiation of the germ layer into distinct membranes. Baer’s description of the formation of the germ layers is very similar to Pander’s. However, where Pander distinguished three germ layers, Baer’s primary differentiation leads to a total of four membranes. The process begins with the separation of the germ layer into two different layers: a superficial ‘‘animal’’ or somatic layer (animalisches Blatt) and an underlying ‘‘vegetative’’ layer (vegetatives Blatt) (Baer 1967, II, p. 46).12 A further differentiation takes place within these two layers: the animal layer separates into a skin layer (Hautschicht) and a muscle layer (Fleischschicht); the vegetative layer is differentiated into a vessel layer (Gefa¨ssblatt) and a mucous layer (Schleimblatt) (which, as Baer explains, correspond to Pander’s layers with the same names) (see Baer 1967, II, p. 46). In the course of further development, the skin layer gives rise to the embryo’s skin and the amnion, while a further differentiation generates the nervous system and the sense organs. From the muscle layer, the muscles and bones develop. The vessel layer is the origin of the main blood vessels. The mucous layer, which is the furthest inside of all the layers, finally forms the intestinal system (Baer 1967, I, p. 154). In a second step, the primary differentiation also includes the folding of the individual membranes into tubes. These tubes represent the main organ systems, from which the different organs will later form (Baer 1967, I, p. 164). Starting from the innermost and moving outwards, Baer distinguishes five tubes. First is the intestinal tract, ‘‘a tube for the assimilation and transformation of matter taken in from the outside world;’’ then the mesentery, ‘‘a tube surrounding the intestinal tract and lengthened to the outside for the movements of the new material intaken.’’ Next is the muscle layer, ‘‘a twin tube for the animal’s movements,’’ followed by the neural tube, responsible ‘‘for its inner life, its desires and emotions,’’ and finally, and most outward, is the skin: ‘‘a tube serving as the boundary against the outside world’’ (Baer 1967, II, p. 74). The formation of tubes is a process of folding that is repeated in the individual layers, from the tube furthest out (the skin) to the one furthest inside (Baer 1967, I, pp. 154–155). The formation of the layers and their 12 The animal and the vegetative layers differ in the way the vesicles are formed in them: in a thin upper membrane and a lower, thicker, but less cohesive membrane (Baer 1967, I, 9).
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folding into tubes concludes the primary differentiation (Sonderung), resulting in the formation of the fundamental organs as rudiments of the various future organs. In a further differentiation, called morphological differentiation, the fundamental organs (tubes) first become more specialized and form the ‘‘primordial organs’’ (Primitivorgane), then further differentiate into the final organs of the embryo. The morphological differentiation thus differentiates ‘‘the primordial organ into heterogeneous forms’’ (Baer 1967, II, p. 79). This occurs through the individual differentiation of various sections of the tubes, ‘‘hence the neural tube separates into sense organs, the brain and the spinal cord, the mucous tube [Schleimhautro¨hre] into the mouth cavity, the oesophagus, the stomach, the intestine, the respiratory organs, the liver, the allantois etc.’’ (Baer 1967, I, p. 155). This morphological differentiation follows ‘‘certain general rules’’ (Baer 1967, II, p. 79), notably the rule stating that the formation of organs occurs through the increased or reduced growth of the individual layers (Baer 1967, I, p. 155). Different rates of growth, taking place to a greater or lesser extent in different parts of the layer, can bring about very different morphological effects—such as ‘‘budding’’ (Abschnu¨rung), or ‘‘protrusion’’ (Hervorstu¨lpung). Baer also spoke of the ‘‘modified growth’’ which took place ‘‘in a larger or smaller part of its extension’’ (Baer 1967, II, p. 80). The difference between the individual organs in position and form is largely the result of the locally and spatially differentiated nature of this growth. Thus, for example, expansion of a section of a tube along its circumference gives rise to organs like the brain or the skull; if, on the other hand, the same tube expands along its longitudinal axis, this will result in the thinning of the layer and give rise to the formation of organs such as the oesophagus or the spinal cord (depending on the tube). Finally, if a development is restricted to a small segment of the tube a growth or protrusion occurs, as is characteristic of the spinous process (ibid.). The main factors determining the morphological structure of the final organs are therefore the location of growth and its direction, the kind of growth involved and its extent. The third form of differentiation, the histological differentiation, is the one Baer elaborates least. He merely states that it describes a differentiation within membranes. There, the texture of the tissue is formed ‘‘by cartilage, muscle and nerve mass separating, part of the mass becoming liquid and passing over into the course of the blood’’ (Baer 1967, I, p. 154). Overall, the histological differentiation organizes ‘‘the separation occurring in the embryo into manifold tissues’’ (Baer 1967, II, p. 92). Thus ‘‘the primary, the morphological and the histological differentiation repeat the same differentiations, the first above each other, the second behind each other, and the third into each other’’ (Baer 1967, II, p. 94). Although Baer analytically distinguishes three forms of differentiation, in practice they are intertwined. In particular, the differentiations do not strictly follow a temporal order. Hence, at no time do the tubes exist as completely formed structures, as the morphological or histological differentiation begins before the primary differentiation is complete (see Baer 1967, II, p. 79). Secondly, the three forms of differentiation by no means always affect the changes of the membranes as a whole. The formation of the individual organs from the tubes, especially, is locally restricted to individual segments of the membranes to be folded into tubes. Thirdly, similar structures are formed by different differentiations, so that the generation of the blood system by
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primary differentiation in the vessel layer does not imply that blood and blood vessels may not also be produced by the histological differentiation in any of the other layers. Pander had stressed that the entities subject to the folding process should not be thought of as ‘‘lifeless membranes’’ expressing ‘‘mechanically formed folds,’’ but as ‘‘of organic origin,’’ spatially differentiable due to the increase in the number of corpuscles. It would thus be wrong to compare the organic folding with that of a sheet of paper, in which ‘‘the whole sheet of paper takes part’’ (Pander 1817, p. 40). In the embryo, it is not the entire membrane that folds, but parts of it, set off by locally unequal organic growth. In the germ layer (see Baer 1967, II, p. 43) and the following layers, ‘‘the top surface develops more quickly than the bottom one, the middle part more quickly than the circumference and the front end more quickly than the rear end’’ (Baer 1967, I, p. 174). Baer thus envisions the movements that form the membranes into structures as being temporally and spatially coordinated: resembling a series of single waves, they form a complex rhythmical pattern, according to which—simultaneously and consecutively, in one or other membrane, at one or the other end or at only one point, but always choreographed as a joint ensemble—they run through the different levels and axes of the developing body, its future shape crystallizing in pulsation. For Baer, therefore, development does not just happen through repetition, but is a relation of repetitions: a ‘‘series of metamorphoses of the individual,’’ as he put it (Baer 1967, I, p. XIX).
4 Rhythmical arts The idea of rhythm as an order of organic time was part of the general tendency in the period around 1800 to conceive of nature as a rhythmical organization and hence to give a rhythmical form to representations of nature. However, discussing rhythm in this period, we must avoid the anachronistic assumption of a divide between the human sciences and the natural sciences. The claim that the episteme of rhythm around 1800 was used in various areas of knowledge and culture should not be interpreted in terms of influence and reception of ideas, for example from physiology to poetology or vice versa (for this standard view, see Hegener 1975; Mahoney 1980; Holland 2009; Mu¨ller-Sievers 2005). My argument in this paper is, rather, that rhythm designated a deeper epistemic layer. It offered an answer to the quest for a rule according to which both nature and culture (thus human beings) generate their products. In both cases, rhythm stood for the ability to keep order while at the same time enabling variation and diversity. In this sense rhythm was both an epistemological and an aesthetic category, while also making that very distinction superfluous. Perhaps surprisingly, rhythm was a relatively new concept in music theory around 1800. Even more surprising may be the fact that in music theory, as well, the new episteme of rhythm was largely a biologically inspired episteme.13 13
For a more detailed discussion of music theory and aesthetics, see Wellmann (2010).
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The single most influential music theory around the turn of the eighteenth century was probably the Akzenttheorie put forth in the work of the philosopher Johann Georg Sulzer and the two composers or music theoreticians Johann Abraham Schulz and Philipp Kirnberger. Central to the Akzenttheorie was the conceptual distinction between metre, as a mechanical measure, and rhythm, as a physiologically derived concept that related to the underlying order of both the organic world and musical movement. The Akzenttheorie conceived of music as a series of identical impulses that is varied, by accentuation, into the diversity of musical expression. Accordingly, metre represents the rigid, counted hierarchy based on the division and separation of musical length. By contrast, rhythm transforms physical movements into the movements of music. For this reason, Kirnberger argued, only the ‘‘external and, as it were, mechanical’’ nature of rhythm could be described (Kirnberger 1968, II, p. 152). Yet the special quality of rhythm was that ‘‘the ear grasped it at once’’ (Kirnberger 1968, II, p. 138). Here, Kirnberger stresses the sensual and physiological ties of rhythm that make it so direct. Despite the absence of rules, rhythm is clearly comprehensible in physiological terms. As a result of this tie to physiological disposition, rhythm has ‘‘the greatest force in music’’ (Kirnberger 1968, II, p. 142). A similar understanding of the role of rhythm can be found in aesthetic theory in general, and prosody in particular, around 1800. A paradigmatic example is the work of the German author and literary critic Karl Philipp Moritz. Moritz’s idea of the autonomous work of art was one of the salient aesthetic conceptions of the age (see Saine 1971; Schrimpf 1980; Allkemper 1990). In his Versuch einer deutschen Prosodie of 1786, Moritz applied his notion of aesthetic autonomy to language and explained how in poetry language is perfected into the work of art. In the transition from prose to poetry, that is, to the work of art, rhythm plays a constitutive role: poetry attains its independence as a work of art solely through the relational order of rhythm, which dissolves the semantic connection of the word and replaces it with the relation of syllables (see Moritz 1975). Here we see the extent to which Moritz’s concept of rhythm partakes in a wider view of the underlying order of the living world. The order of rhythm elevates language to the status of the autonomous work of art thanks to its organic qualities. Furthermore, Moritz’s concept of the autonomy of artistic productions is constructed in analogy to the autonomous order of nature. Moritz paints a picture of a permanently self-destroying and re-forming nature (Moritz 1962). Life perpetually and continuously emerges anew as individual structures are isolated from the whole and then restructured into a new context. The highest form of this kind of formation is sexual reproduction. The embryo obtains through its own ‘‘movement … its own centre of gravity and the axis of its rotation in itself’’ (Moritz 1962, p. 97). Embryonic movement is envisioned here as a dual process: first, the emergent embryo increasingly isolates itself from the mother’s body through its own bodily movements. The beginning of the embryo’s independent life is marked by the ability to move its own limbs. But independent physical movement is only the beginning of development. In a second step, organic formation means a development into ever higher forms of movement. The highest form of movement, the ultimate goal of this process, is not physical but linguistic movement
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(Sprachbewegung). From physical movement, the development stretches ‘‘to where the gentlest movement, in the true tool of language, becomes language itself’’ (Moritz 1962, p. 98). As a living creature, the embryo becomes more independent the more it is able to ‘‘speak through itself’’—first through its physical and later through its linguistic movements. The body ‘‘speaks’’ through its movement just as the moment of movement is constitutively retained in language, for ‘‘in what lives and thinks, formation, movement and sound are determined—causing the whole to dissolve again in harmony, the all-encompassing again encompassing itself’’ (Moritz 1962, p. 98). Secretion, movement and sound (Absonderung, Bewegung, Laut)—that is, according to Moritz, the triad of man’s perfection, his inner order and determination, the rhythm of his development. Moritz thus incorporates a theory of embryogenesis with a theory of language: just as embryonic life emerges by forms becoming isolated and independent of a homogeneous mass, so syllables are separated from the context of the word. Then movement creates a new context between the resulting forms. What is important here is that the course of development cannot be deduced from the single form. Instead, it is only the law of the new order that constitutes the new organism’s independence and autonomy (Autonomie und Eigengesetzlichkeit). This law of development is its rhythm, which perfects itself from the bodily movement, via the linguistic movement, up to the point of poetic art. For Moritz, as for many other of his contemporaries around 1800, the time of the development of an organism is thus not linear and chronological time, but rhythmical time. Organic time is reciprocal and irregular, and it expresses itself in constant restructuring through repetition and renewal, generation and disintegration and regularity and change. It takes shape as an autonomous entity as a result of its own structuredness—embedded in the chronological flow of time, but simultaneously separated from it. The rhythmical structure is able to bring about the infinite abundance of organic forms by linking the economy of repetition to the moment of variation. The variation of rhythm can begin at any point along a discrete sequence, which means that nature is always able to operate on the border of disorder, at the limit of disarray, even at the edge of break-up. It is the constant resetting of rhythmical order that keeps the becoming organism balanced between continuation and deviation. Thus the creative elements of the generative and formative aspects of nature are to be found not in its mere progress, but in the game of repetition, the interaction between continuity and discontinuity, rule and deviation, order and chaos. The ever new forms of becoming do not emerge without laws, but on the basis of the previous rhythmical series, which simultaneously varies them into new forms in the course of their continuation.
5 Conclusion Corpuscles that flow and solidify into forms in their movement; membranes that fold and turn into tubes; tubes that thicken or taper at points; an embryo that becomes an autonomous living organism through the movement in and of its body; and, finally, the living human who is able to transform physical motion into complex
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linguistic movements and even to elevate it to the spheres of aesthetics in poetry— around 1800, the emerging organism and organic life in general have been reconceptualised, in terms of rhythmic motion, as an uninterrupted, continuous, constantly new, but never disorderly motion. The story of the episteme of rhythm around 1800, as I have attempted to sketch it in this paper, offers a new perspective on the epistemology of embryology in particular and biology in general. I have argued that temporalization is not a sufficient answer to the question of how development was understood around 1800. Instead, the new epistemology of rhythm, simultaneously conceived in various fields of knowledge, framed the generation and formation of the living as an order of time. Rhythm was considered to be the law under which nature’s temporal dimension unfolded. Development became both rule and variation—and this is what made up its aesthetic as well as epistemological momentum.
References Adelmann, H. B. (1966). Marcello malpighi and the evolution of embryology. Ithaca: Cornell University Press. Allkemper, A. (1990). A¨sthetische Lo¨sungen. Studien zu Karl Philipp Moritz. Munich: Fink. ¨ ber Entwickelungsgeschichte der Thiere: Beobachtung und Reflexion. Baer K.E. [1828/1835] (1967). U Erster Theil mit drei colorirten Kupfertafeln, Ko¨nigsberg 1828. Zweiter Theil mit vier Kupfertafeln, Ko¨nigsberg 1835, facsimile reprint, Brussels: Culture et Civilisation. Baer K.E. [1866]. (1972). Nachrichten u¨ber Leben und Schriften des Herrn Geheimraths Dr. Karl Ernst von Baer, mitgeteilt von ihm selbst; vero¨ffentlicht bei Gelegenheit seines fu¨nfzigja¨hrigen DoctorJubila¨ums am 29. August 1864 von der Ritterschaft Ehstlands, 2nd ed., facsimile reprint of the 1886 ed., Hannover-Do¨ren: Hirschheydt. Benveniste, E. (1966). Proble`mes de linguistique ge´ne´rale, 2 vols. Paris: Gallimard. Brauckmann, S. (2011). Axes, planes and tubes, or the geometry of embryogenesis. Studies in History and Philosophy of Biological and Biomedical Sciences, 42, 381–390. Churchill, F. B. (1991). The rise of classical descriptive embryology. In S. F. Gilbert (Ed.), A conceptual history of modern embryology (pp. 1–29). Baltimore: Johns Hopkins University Press. Detlefsen, K. (2006). Explanation and demonstration in the Haller-Wolff debate. In J. E. H. Smith (Ed.), The problem of animal generation in early modern philosophy (pp. 235–261). Cambridge: Cambridge University Press. Do¨llinger, I. (1821). ‘‘Kreislaufe des Blutes,’’ In Denkschriften der ko¨niglichen Academie der Wissenschaften zu Mu¨nchen fu¨r die Jahre 1818, 1819 und 1821. Classe der Mathematik und Naturwissenschaften, VII: pp. 169–228. Foucault, M. (1974). The order of things: An archaeology of the human sciences. London: Routledge. Gasking, E. B. (1967). Investigations into generation 1651–1828. London: Hutchinson. Gilbert, S. F. (Ed.). (1991). A conceptual history of modern embryology. Baltimore: Johns Hopkins University Press. Hegener, J. (1975). Die Poetisierung der Wissenschaften bei Novalis dargestellt am Prozeß der Entwicklung von Welt und Menschheit. Studien zum Problem enzyklopa¨dischen Welterfahrens. Bonn: Bouvier. Herrlinger, R. (1959). C. F. Wolffs ‘Theoria generationis’ (1759). Die Geschichte einer epochemachenden Dissertation. Zeitschrift fu¨r Anatomie und Entwicklungsgeschichte, 121, 245–270. Holland, J. (2009). German romanticism and science. The procreative poetics of Goethe, Novalis, and Ritter. New York: Routledge. Jahn, I. (1998/1999). Wer regte caspar Friedrich Wolff (1734–1794) zu seiner Dissertation Theoria generationis (1759) an?’’ Philosophia Scientiae, Cahier spe´cial 2: pp. 35–54.
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Folding into being Wellmann, J. (2010). Die Form des Werdens. Eine Kulturgeschichte der Embryologie, 1760–1830. Go¨ttingen: Wallstein. Witt, E. (2008). Form—a matter of generation: The relation of generation, form, and function in the epigenetic theory of Caspar F. Wolff. Science in Context, 21(4), 649–664. Wolff, C. F. (1812). U¨ber die Bildung des Darmkanals im bebru¨teten Hu¨hnchen. Uebersetzt und mit einer einleitenden Abhandlung und Anmerkungen versehen von Johann Friedrich Meckel. Halle: Renger. Wolff, C. F. [1759] (1896) Theoria Generationis. 2 vols: Erster Theil: Vorrede, Erkla¨rung des Plans, Entwicklung der Pflanzen; Zweiter Theil: Entwicklung der Thiere, Allgemeines Uebersetzt und herausgegeben von Paul Samassa, Leipzig: Engelmann.
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Folding into being: early embryology and the epistemology of rhythm Janina Wellmann
Received: 8 July 2014 / Accepted: 16 November 2014 Springer International Publishing AG 2014
Abstract Historians have often described embryology and concepts of development in the period around 1800 in terms of ‘‘temporalization’’ or ‘‘dynamization’’. This paper, in contrast, argues that a central epistemological category in the period was ‘‘rhythm’’, which played a major role in the establishment of the emerging discipline of biology. I show that Caspar Friedrich Wolff’s epigenetic theory of development was based on a rhythmical notion, namely the hypothesis that organic development occurs as a series of ordered rhythmical repetitions and variations. Presenting Christian Heinrich Pander’s and Karl Ernst von Baer’s theory of germ layers, I argue that Pander and Baer regarded folding as an organizing principle of ontogenesis, and that the principle’s explanatory power stems from their understanding of folding as a rhythmical figuration. In a brief discussion of the notion of rhythm in contemporary music theory, I identify an underlying physiological epistemology in the new musical concept of rhythm around 1800. The paper closes with a more general discussion of the relationship between the rhythmic episteme, conceptions of life, and aesthetic theory at the end of the eighteenth century. Keywords
Rhythm Rhythmic episteme Embryology Development Folding
1 Introduction In the history of biology, the time around 1800 is usually considered as marking the beginning of the modern life sciences, highlighted by the move from a preformationist theory of generation to the new theory of epigenesis focusing on J. Wellmann (&) Leuphana Universita¨t Lu¨neburg, MECS – Medienkulturen der Computersimulation, Wallstraße 3, 21335 Lu¨neburg, Germany e-mail: [email protected]
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the process of the gradual development of the embryo. Pivotal to this story is the work of the German Caspar Friedrich Wolff, notably his epoch-making work Theoria generationis of 1759. The significance of this work for the history of embryology can hardly be overrated. In it, Wolff endeavoured to do nothing less than conceive a new theory of organic development, which went far beyond contemporary views pro and contra epigenesis or preformation. Following Wolff, at the beginning of the nineteenth century Christian Heinrich Pander and Karl Ernst von Baer developed the theory of germ layers—until today the basis of modern embryology.1 By the third decade of the nineteenth century, the foundations of modern embryology, as the science of development, had largely been laid. But what is development? How was development envisaged by Wolff, Pander and Baer, and what was new in their approach? Merely to say that their views were ‘‘epigenetic’’ hardly helps understand the underlying epistemology of their work. For example: What was behind Wolff’s claim that the embryo only gradually forms from an originally homogeneous mass? Why did Pander and Baer decide to trace all development back to the formation of four germ layers? And most importantly: What was development for them? How did they investigate it, observe it, represent it? Historiography has customarily regarded the emergence of the epigenetic theory of development and embryology around 1800 as a part of a new world view often described as ‘‘temporalization’’ or ‘‘dynamization’’. The end of the ‘‘representation’’ of the classical episteme as a ‘‘form of simultaneity’’—as Michel Foucault put it in The Order of Things (Foucault 1974, 337)—marked a breach in the entire order of knowledge towards the end of the eighteenth century. From then on, ‘‘a profound mass of time’’ was precipitated into the ‘‘old flat world of animals and plants, engraved in black on white’’ (Foucault 1974, p. 138). Largely following Foucault, Wolf Lepenies in his Ende der Naturgeschichte formulated the adage of the ‘‘empirical imperative’’ resulting from the ‘‘pressure of experience and observation.’’ According to this thesis, the temporalization of nature became inevitable as soon as the mass of the new knowledge threatened to burst the horizontal level of space (Lepenies 1976, p. 18; see also Lovejoy 1936; Koselleck 1975; von Engelhardt 1979; Richards 2002; Stockhorst 2006). But is ‘‘temporalization’’ a sufficient answer to the question of how development was understood around 1800? Mere progress in time does not seem to be an adequate explanation for the new understanding of biological development in this period. Obviously, organisms were considered to have a temporal dimension long before 1800. Even the theories of preformation had by no means denied progressive change. In fact, the new questions that were asked in the late eighteenth century went far beyond the temporalization of biological processes; they touched upon the underlying dynamics of the temporal. When scientists of that period gazed through the microscope, observed hens’ eggs and dissected organisms, prepared them and compared them with one another, they increasingly realized (and tried to capture) the ambiguous nature of the living world: on the one hand well-ordered, a 1
On the history of embryology, see; Needham (1959), Adelmann (1966), Gasking (1967), Roger (1963), Roe (1981), Gilbert (1991), Oppenheimer (1967), Smith (2006).
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functioning realm, on the other permanently changing, in transition, every form simultaneously structure and the disintegration of that structure. In particular, they asked how the nascent organism developed into a highly complex structure while its parts and its whole changed uninterruptedly. This paper posits that the episteme of rhythm provided an answer to these questions. Unique and essentially new in the conceptualization of development around 1800 was its underlying rhythmical epistemology. Rhythm may be a temporal structure, but unlike the continuous flux of time, it implies the restriction of the flux in favour of a rule.2 Indeed, it was this very feature that explained the power of rhythm around 1800: rhythm’s ability to structure temporal processes. Rhythm did not suspend time, but subjugated it. It subjected to a rule the incessant change to which organic becoming was exposed. Thus, around 1800 nature was not merely conceptualized as temporal and changeable. In fact the contrary was the case: rhythm was considered to be the law under which nature’s temporal dimension could be unfolded. Hence establishing a science of becoming did not imply imagining the organism as an essentially dynamic and temporal entity, but as a being whose most important manifestation is order under the condition of temporality. Rhythm thus described the generation and formation of what is living as an order of time. This paper argues for the central role of the rhythmical episteme in the establishment of the science of embryology around 1800. In the first section, I show how Caspar Friedrich Wolff’s epigenetic theory of development was based on a rhythmical conception, namely the hypothesis that organic development occurred as a series of ordered rhythmical repetitions and variations. The second section is devoted to Pander’s and Baer’s theory of germ layers. Central to this theory is the idea that the entire development of the embryo occurs as a gradual differentiation of primary germ layers. One central aspect of Pander’s and Baer’s work, an aspect that has hitherto almost entirely escaped the attention of scientists and historians, is the principle of the fold.3 As I will show, Pander and Baer made folding an organizing principle of ontogenesis: all the changes in the egg during early embryonic development, in their view, take place as a series of foldings of the germ layers. The explanatory power of this scheme, I maintain, stems from the understanding of folding as a rhythmical figuration. In my discussion of the embryological investigations of Wolff, Pander and Baer, I use the concept of rhythm mainly as an analytical category. More generally, though, I argue that the concept of biological development after 1800 (and essentially up to the present day) is fundamentally rhythmical. However, my 2 Usually, the Greek word rhythmos is considered to derive from the root rhe´ein, ‘‘flow,’’ ‘‘protect,’’ but alternative derivations have also traced the concept to ‘‘draw’’ or ‘‘fend off’’ as well as ‘‘protect.’’ In his seminal study, Emile Benveniste substantiated the etymological proximity of the concept of rhythm to the meanings ‘‘shape’’ and ‘‘form’’ or ‘‘figure.’’ Benveniste speaks of rhythm as the ‘‘shape of the fleeting and changeable’’ or the ‘‘order of time’’ (Benveniste 1966, I, 326–335); for the etymology, see also (Trier 1949; Seidel 1976, 15; Seidel 2003). 3
Whereas the history of biology has consistently acknowledged Pander and Baer as the authors of the theory of germ layers, this aspect of their work has gone practically unnoticed (see, for example, Churchill 1991; Oppenheimer 1963; Raikov 1968, 1984; Brauckmann 2011). Schmitt calls the concept of the fold an ‘‘avance´e conceptuelle considerable,’’ but does not go into detail (Schmitt 2003, 161).
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argument is also a more specific historical one. I maintain that it was not a coincidence that biologists around 1800 attempted to understand the living world in rhythmical terms. In fact, around 1800 the idea of rhythm and especially the claim that life is essentially rhythmic can be found not only in embryology, but also in many other fields of knowledge. The idea of a rhythmically organized nature was based on an episteme of rhythm that was simultaneously the basis of new aesthetic concepts in the era’s poetology and music theory as well as expressing itself in other scientific theories. This is the subject of the third part of this paper. There I briefly discuss the notion of rhythm in contemporary music theory and stress the physiological epistemology of the new musical concept of rhythm. Finally, I touch upon the more general aspect of aesthetic theories around 1800 by discussing the work of Karl Philipp Moritz, who formulated one of the most influential aesthetic concepts of the time, notably his notion of ‘‘aesthetic autonomy.’’4
2 Repetition, pulse, spiral Most accounts of Caspar Friedrich Wolff’s theory of generation focus on his early writings, notably his doctoral thesis of 1759 (Wolff 1896), and tend to place his work in the context of the debate on epigenesis versus preformation (Schuster 1936; Uschmann 1955; Herrlinger 1959; Jahn 1998/1999; Mocek 1995; Witt 2008). However, if we widen the perspective to include Wolff’s later work, and attempt a more careful reading of his embryological observations, a new understanding of his epistemology emerges. In particular, I argue that Wolff conceived of the genesis and development of the embryo as the interplay between three moments: repetition, pulsation, and spiral motion. De facto they are linked, and as a unity form the complex structure of Wolff’s rhythmical episteme of epigenesis. In Wolff’s work, we find the episteme of rhythm framed as a continuous movement or flow, which at the same time is an ordered and controlled movement composed of several components or sub-movements. It is the ability to structure the flow in various ways by alternating the order of the sub-movements which stands at the heart of Wolff’s epigenetic imagery. The rhythmic variation is based on three elements: repetition, pulsation and spirality. Wolff’s point of departure is the search for a universal principle of all processes of organic formation (Bildung). Wolff assumes that such a principle should underlie not only embryogenesis but practically all physiological processes. Nutrition, growth or reproduction are therefore not distinct physiological events, but merely variations of the same underlying theme. The vital processes of the organism are to be regarded as one and the same basic constellation that is constantly repeated, but varied in the repetition—for example when the processes take place temporally or geographically offset, in isolation or continuously. Only the specific 4
My book, Die Form des Werdens. Eine Kulturgeschichte der Embryologie, 1760–1830 (Wellmann 2010), presents in more detail the simultaneous emergence of a new treatment of the organic in several different disciplines such as music theory, poetology, philosophy, aesthetics, embryology, physiology and botany.
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circumstances ‘‘accompanying this process’’ (Wolff 1896, I, Sect. 25, p. 8) determine whether a process is called nutrition, growth or reproduction.5 Secondly, epigenetic development is pulse, pulsating—the continuous alternation between two states. Here my reading of Wolff’s work significantly differs from that of existing scholarship. It is commonly claimed that the central features of Wolff’s epigenesis were his emphasis on the homogeneous and amorphous beginning of development, and the gradual emergence of structures out of this state. In addition, Wolff is said to have postulated a force guiding this development—the ‘‘essential force’’ or vis essentialis (see Witt 2008, p. 650; Roe 1981, p. 103; Oppenheimer 1967, p. 141; Gasking 1967, pp. 97–106; Detlefsen 2006). However, no attention has been paid to how Wolff viewed the interaction between force and matter, which I argue was as a rhythmical dynamic of flow and standstill. At the very beginning of his thesis, Wolff introduces this elementary idea, on which all his further considerations on development are based: he traces all vital processes back to the same basic movement, the constant interaction between the flowing and solidification of plant and animal fluids. Nutrition, growth and development can all be reduced to the oscillation of nutritive fluid (Na¨hrsaft) between movement and standstill. Wolff underlines the fundamental claim of this approach in two ways: not only can all vital processes be traced back to this movement, but—and this generalization is essential for Wolff’s approach—it applies both to plants, discussed in the first part of the dissertation, as well as animals, which Wolff treats in the second part. For Wolff, the mutually conditioning interaction of the movement and stasis of organic fluids is a sufficient grounding for the formation of any structure in the organism. Thus, flowing alone does not explain how the nutritive fluids coagulate and the formation of structures comes about. Interruptions and breaks are also necessary, as ‘‘only as a result of stasis does the fluid [Flu¨ssigkeit] begin to thicken and gradually deposit solid parts’’ (Wolff 1896, I, Sect. 35, p. 23). The break in the flow, the pause, the interruption of the flux is the real moment of development, for ‘‘in a state of standstill the nutritive fluid can easily deposit something of its mucous substances [schleimige Stoffe] … in vesicles [Bla¨schen] here and there’’ (Wolff 1896, I, Sect. 36, p. 23). Wolff goes a step further by qualifying the movement of the nutritive fluid more precisely: the rhythm of the fluid’s movement determines the specific form of the structures formed. The very first structures that can be identified in the liquid are vesicles and vessels. Fluids in motion form vessels. These, in turn, when they come to a standstill and are deposited, are responsible for the formation of vesicles (Wolff 1896, I, Sect. 41, p. 27, Sect. 23, p. 18, Sect. 28, p. 20). In addition, a slow flow produces ‘‘regular’’ structures, whereas the alternation between stagnation and flow generates ‘‘irregular cell membranes’’ (Wolff 1896, I, Sect. 35, p. 23). The third element in Wolff’s concept of rhythmical development is that of the spiral, that is, variation within repetition. Wolff’s notion of spiral development, as ¨ ber die Bildung des Darmkanals im bebru¨teten elaborated mainly in his work U Hu¨hnchen of 1768 (Wolff 1812), would become tremendously influential on the 5
Here and throughout, all translations are my own unless stated otherwise.
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development of embryology, notably on the work of Christian Pander and Karl Ernst von Baer (discussed below).6 The basic tenet of Wolff’s 1768 work is that organs do not develop independently of each other, but always as parts of whole organ systems. Moreover, all organ systems are formed in the same way, namely by membrane folds. Each and every developmental path is nothing but a series of repeating folds. The peculiar series of foldings at different points of time bring about a gradual differentiation into specific organs. Wolff observed that initially the two surrounding membranes bend and fold, grow together at the edges and form the three sections of the intestinal system, as a result of this movement and contraction (Wolff 1812, pp. 132–133). However, these forms do not lead directly to the intestinal tract in its final form. On the contrary, Wolff observed that the existing forms were replaced by completely new structures after the end of the fifth day, triggered off by a new sequence of folds (Wolff 1812, pp. 183–184, 187). Through a series of meticulous observations, Wolff showed how the intestinal tract is practically formed and deformed, structured and restructured several times by the repeated formation and disintegration of different membranes. In other words, embryogenesis is not a simple linear generative process, but a back and forth of construction and destruction of forms through repeated folding. With the elements briefly sketched here, Wolff set embryology on completely new foundations. His approach was based on tracing development back to the elementary phenomenon of movement. The specific qualities of organic development result from the rhythmical, pulsating constellation of movement and stasis, repetition and variation, stability and change.
3 Membranes, tubes and foldings The physiology of the eighteenth and the early nineteenth centuries described the basic substance of the organic as ‘‘mucous’’ and amorphous on the one hand, and on the other as manifesting some kind of basic structure—descriptions varied, and included ‘‘grains’’ and ‘‘corpuscles,’’ ‘‘vesicles,’’ ‘‘globules’’ or ‘‘cellular tissue’’ (Do¨llinger 1821).7 The detection of the stages of development from the seemingly unstructured fertilized chicken egg to a fully developed embryo stood at the centre of the groundbreaking work Beitra¨ge zur Entwickelungsgeschichte des Hu¨hnchens im Eye published by Christian Heinrich Pander in 1817 (Pander 1817). Working under the guidance of the Wu¨rzburg physiologist Ignaz Do¨llinger, the young Pander gave special attention to the transition from freely moving ‘‘granules’’ or ‘‘corpuscles’’ (Ko¨rnchen) to structured layers or membranes. The importance of this step, the conceptualization of embryogenesis in terms of layers and membranes, can hardly be overestimated. It gave embryology a new 6
Wolff’s doctoral thesis Theoria generationis aimed to provide a theory of the development of basic organized structures from homogeneous, amorphous matter. In his later work on the genesis of the intestinal tract (De formation intestinorum, written in Latin in 1768 and published in a German translation by Johann Friedrich Meckel in 1812), Wolff went one step further and focused on one organ to trace the formation of complex organic structures from already existing, simple formations.
7
Not to be confused with ‘‘cells,’’ discovered only in the late 1830s.
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conceptual and visual language that by and large still underlies the science 200 years later. As I will argue in the following, Pander’s ability to describe development in terms of the folding of membranes relied heavily on an underlying rhythmic epistemology. In order to grasp this epistemology, I analyse in some detail key passages from Pander’s (1817) publication. 3.1 From corpuscles to layers Pander’s point of departure is the non-incubated fertilized egg, in which he describes the germ layer as initially consisting ‘‘of a simple layer made of interconnected corpuscles’’ (Pander 1817, p. 5). After 12 h they have formed two layers, slightly detached, enough so for Pander to discern two distinct layers—he calls them the serous layer (sero¨ses Blatt) and the mucous layer (Schleimblatt). They are distinguished by the different structures of the vesicles from which they were formed—a coarse grainy structure on the inside and a more homogeneous form on the outside (Pander 1817, pp. 6–7). After about 20 h of incubation, a further metamorphosis of the germ layer commences, leading to the formation of a third layer between the two already existing ones: the vascular layer (Gefa¨ßhaut). This layer also arose in the formation of the grainy mass of organic material (Pander 1817, pp. 13–14). Thus after 24 h the germ layer consists of three membranes, forming the basis for the emergence of all other forms in the egg. Everything that now happens in the egg must be seen as ‘‘never for anything else but a metamorphosis of this membrane and its layers [Bla¨tter], endowed with the inexhaustible abundance of the formative drive [Bildungstrieb]’’ (Pander 1817, p. 6). 3.2 From layers to folds From this point on, Pander makes the spatial shifts of the germ layers the organizing principle of the formation of new structures in the fertilized egg. In particular, he aspires to understand the underlying logic of the movements of these membranes, their warps, their changes, their gradual moving towards and away from each other, or their coalescence into one membrane. All these processes, Pander believes, can be understood in terms of a single dynamic, namely that of folding.8 Pander distinguished three kinds of folds. The first fold takes place in the mucous and the serous layers, which begin to fold after 18 h of incubation. This first fold produces the primitive streak with its two primitive lateral folds (Primitivfalten). They mark the beginning of the embryo. In the germinal area (Keimhof), the 8
The germ layer ‘‘itself forms the body and the intestines [Eingeweide] of the animal solely through the simple mechanism of folding. A tender thread attaches itself as a spinal cord, and no sooner has this happened than it forms the first folds, which even have to show the spinal cord its location, as a cover over the precious thread, this way forming the first basis for the body. Then it makes a new fold, which, unlike the first, fills the abdominal and thoratic cavities [Bauch- und Brustho¨hle] with content. And it sends out folds for the third time to wrap the foetus formed from it and by it in suitable envelopes [Hu¨llen]. So nobody should be amazed if there is so much talk of folds and changes in the course of our narration’’ (Pander 1817, 7).
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primitive streak initially develops as parallel folds, which then unite in an arch at the top end and remain open at the bottom (Pander 1817, p. 8). The future head of the embryo is produced at the closed end of the fold. Subsequently, the primitive folds envelop the beginnings of the spinal cord by turning over at their joint end (Pander 1817, pp. 9–10).9 Underlying this succinct description was a highly complicated process of folding, the explanation of which posed one of the greatest challenges in Pander’s investigation. Essentially, Pander describes the process in the following way: the approach and unification of the primitive folds does not occur abruptly; first, ‘‘the primitive folds are bent in waves along their entire length.’’ Then ‘‘the edges of these folds join’’ in the middle and ‘‘by growing together’’ they form ‘‘a seam that covers the part of the spinal cord below it as a whitish strip.’’ At a later moment, ‘‘the two folds join at the top and bottom.’’ At the lower end, the folds separate at ‘‘an acute angle’’ with the spinal cord visible between them. At the top end, they run in parallel but separately from each other as far as the sickle-shaped fold, then ‘‘they curve like waves,’’ but their edges remain standing ‘‘straight up.’’ In this way, ‘‘spaces or cells’’ develop, increasing in size towards the head region (Pander 1817, p. 10).10 A second folding, this time of the primitive streak, produces two further structures that will later give rise to the oesophagus and the heart. It is important to note that every movement by one of the membranes also affects the others. Therefore, folding takes place on several axes, horizontally and vertically. As the lateral folds continue to approach each other, finally to meet in the middle, there emerges a ‘‘space formed by the descending part of the layer and separated into two pipe-shaped tubes.’’ Of these, each forms a ‘‘sac closed from the top and the sides and open towards the bottom’’ (Pander 1817, p. 12). The first sac marks the origins of the oesophagus and the second those of the heart (Pander 1817, pp. 12–13). In a further metamorphosis, the tube of the heart formed by the folding of the membrane finally changes ‘‘into the completely formed heart’’ through additional ‘‘folding, sometimes binding [Verschnu¨rung], contraction and expansion of its walls’’ (Pander 1817, p. 18).11 9
What Pander observed here (and Baer later realized) was the notochord.
10
‘‘Allein dieses Anna¨hern und die Vereinigung derselben [der Primitivfalten] geschieht nicht auf einmal, so dass sich das Ru¨ckenmark plo¨tzlich unter diese Hu¨lle versteckte; sondern erst werden die Primitivfalten in ihrer ganzen La¨nge wellenfo¨rmig gebogen, und zwar so, dass jede Erweiterung dem Zwischenraume eines jeden Wirbelrudimentes entspricht, und jede Verengerung dem anliegenden, rundlich-viereckigen Ko¨rperchen desselben. Dann legen sich in der Mitte die Ra¨nder dieser Falten an einander, und bilden durch ihr Zusammenwachsen eine Naht, welche als weisslicher Streifen den unter ihr liegenden Theil des Ru¨ckenmarkes bedeckt. Nicht so schnell vereinigen sich die beiden Falten oben und unten; nach unten gehen sie unter einem spitzen Winkel aus einander, und zwischen ihnen zeigt sich alsdann unmittelbar der Faden des Ru¨ckenmarkes mit seiner lanzettfo¨rmigen Endigung; nach oben weichen sie auch unter einem scharfen Winkel von einander ab, laufen aber, bis zum sichelfo¨rmigen Umschlage getrennt, neben einander, kru¨mmen sich wellenfo¨rmig, und indem ihre Ra¨nder nicht eingeschlagen, sondern gerade in die Ho¨he gerichtet sind, entsteht zwischen ihnen eine Reihe von drei bis vier gegen das Kopf-Ende an Gro¨sse zunehmenden Ra¨umen oder Zellen, anscheinend auf jeder Seite von zwei Linien eingefasst, weil die beiden Bla¨tter, woraus jede Falte besteht, als Linien durch ihren Rand durchschimmern‘‘(ibid., 10). 11
For details, Pander refers to work by Haller and the drawings of Malpighi (see Haller 1758; Adelmann 1966).
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Whereas the second folding is taking place in the head region of the primitive streak, the third happens at the bottom or tail end. A few hours after the second folding, a ‘‘similar folding, but different in size and form’’ occurs at the tail end of the foetus (Pander 1817, p. 21 also pp. 23–4). The third folding is ‘‘very similar to the two preceding ones … but now the entire development is turned to the outside and proceeds over the embryo’s back,’’ whereas the two foldings already described ‘‘formed at its ventral side and the folds were turned towards the yolk’’ (Pander 1817, p. 24). The three foldings are similar, in that initially all three layers mutually affect each other ‘‘until the serous layer reaches a stage in which it is able to lead the process on its own’’ (ibid.). The third folding, thus, takes place at the bottom rather than the top end of the primitive streak; it happens at the dorsal rather than the ventral side of the embryo; and it folds to the outside rather than to the inside. Because the folding starts in a different section of the membrane and takes a different direction, what is produced are not the tubular beginnings of the inner organs but the extra-embryonic membranes, in this case the amnion. The two lateral folds gradually grow together along a back-seam (Ru¨ckennaht) from the head to the tail end of the embryo. This produces two cavities. The first Pander calls the ‘‘true amnion,’’ which resembles ‘‘a sac filled with water’’ or a ‘‘bladder’’ (Blase) of the inner layer, which wraps up the foetus ‘‘down to its abdomen.’’ The second is the ‘‘false amnion,’’ formed from the outer layer (ibid.). The false amnion, which can hardly be discerned as an autonomous membrane, replaces the vitelline membrane (Dotterhaut). Another extra-embryonic membrane, the chorion, is similarly produced at the lower end of the foetus —but this only happens once the amnion has reached completion and the intestinal tract has developed enough for the oesophagus and the rectum to be differentiated (Pander 1817, p. 25). By describing the formation of the primitive streak, the intestinal tract, the heart, and the thin layers surrounding the embryo, the amnion and the chorion, Pander provides a comprehensive explanation of the formation of the elementary organ systems in early embryogenesis. His view of this development is based on three rhythmical foldings of the membranes, recurring periodically and repeating themselves at different locations of the developing egg. The foldings are very similar and yet not identical—like rhythmical waves that produce the forms of the future living creature with their movement. 3.3 From layers to tubes ¨ ber Entwickelungsgeschichte der Thiere. Beobachtung und In the first volume of U Reflexion, published in 1828 (Baer 1967), Karl Ernst von Baer described in much greater detail the process of folding that Wolff had imagined and Pander had sketched. For Baer, too, the germ layers were at the centre of his observations and his concept of differentiation. However, Baer considered the movements of the membranes to be so complex that he accepted Pander’s concept of the fold only with reservations. The process could only be presented ‘‘as a fold in a schematic drawing,’’ he wrote in the 1860s (Baer 1972, p. 298). As I argue in the following, Baer did not reject Pander’s fold but expanded it. While Pander imagined it essentially in two dimensions, as a kind of line, Baer imagined a surface or plane
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that is extending, moving, bending, curving and shifting in all three dimensions of space, and also changing shape even on isolated spots of its surface through the accumulation of organic substance. For Baer, formation takes place through a process of segregation or separation (Sonderung), a process that today might refer to a series of differentiations and the formation of specific organs (organogenesis). In particular, Baer distinguishes three kinds of ‘‘Sonderungen’’: (a) the ‘‘primary differentiation’’ or the differentiation into four germ layers, (b) the ‘‘morphological differentiation’’ into primitive organs, and (c) the ‘‘histological differentiation’’ within these layers. Like Pander before him, Baer describes the ‘‘formative tissue’’ (Bildungsgewebe) or the ‘‘basal substance of all animal parts’’ (Grundmasse aller thierischen Theile) as ‘‘albumen-like primitive mucous’’ (eiweissa¨hnliche Grundschleime) consisting of ‘‘partially separated corpuscles,’’ in other words accumulations of corpuscles distributed irregularly in the basal substance (Baer 1967, I, p. 19). Development now commenced with the differentiation of the germ layer into distinct membranes. Baer’s description of the formation of the germ layers is very similar to Pander’s. However, where Pander distinguished three germ layers, Baer’s primary differentiation leads to a total of four membranes. The process begins with the separation of the germ layer into two different layers: a superficial ‘‘animal’’ or somatic layer (animalisches Blatt) and an underlying ‘‘vegetative’’ layer (vegetatives Blatt) (Baer 1967, II, p. 46).12 A further differentiation takes place within these two layers: the animal layer separates into a skin layer (Hautschicht) and a muscle layer (Fleischschicht); the vegetative layer is differentiated into a vessel layer (Gefa¨ssblatt) and a mucous layer (Schleimblatt) (which, as Baer explains, correspond to Pander’s layers with the same names) (see Baer 1967, II, p. 46). In the course of further development, the skin layer gives rise to the embryo’s skin and the amnion, while a further differentiation generates the nervous system and the sense organs. From the muscle layer, the muscles and bones develop. The vessel layer is the origin of the main blood vessels. The mucous layer, which is the furthest inside of all the layers, finally forms the intestinal system (Baer 1967, I, p. 154). In a second step, the primary differentiation also includes the folding of the individual membranes into tubes. These tubes represent the main organ systems, from which the different organs will later form (Baer 1967, I, p. 164). Starting from the innermost and moving outwards, Baer distinguishes five tubes. First is the intestinal tract, ‘‘a tube for the assimilation and transformation of matter taken in from the outside world;’’ then the mesentery, ‘‘a tube surrounding the intestinal tract and lengthened to the outside for the movements of the new material intaken.’’ Next is the muscle layer, ‘‘a twin tube for the animal’s movements,’’ followed by the neural tube, responsible ‘‘for its inner life, its desires and emotions,’’ and finally, and most outward, is the skin: ‘‘a tube serving as the boundary against the outside world’’ (Baer 1967, II, p. 74). The formation of tubes is a process of folding that is repeated in the individual layers, from the tube furthest out (the skin) to the one furthest inside (Baer 1967, I, pp. 154–155). The formation of the layers and their 12 The animal and the vegetative layers differ in the way the vesicles are formed in them: in a thin upper membrane and a lower, thicker, but less cohesive membrane (Baer 1967, I, 9).
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folding into tubes concludes the primary differentiation (Sonderung), resulting in the formation of the fundamental organs as rudiments of the various future organs. In a further differentiation, called morphological differentiation, the fundamental organs (tubes) first become more specialized and form the ‘‘primordial organs’’ (Primitivorgane), then further differentiate into the final organs of the embryo. The morphological differentiation thus differentiates ‘‘the primordial organ into heterogeneous forms’’ (Baer 1967, II, p. 79). This occurs through the individual differentiation of various sections of the tubes, ‘‘hence the neural tube separates into sense organs, the brain and the spinal cord, the mucous tube [Schleimhautro¨hre] into the mouth cavity, the oesophagus, the stomach, the intestine, the respiratory organs, the liver, the allantois etc.’’ (Baer 1967, I, p. 155). This morphological differentiation follows ‘‘certain general rules’’ (Baer 1967, II, p. 79), notably the rule stating that the formation of organs occurs through the increased or reduced growth of the individual layers (Baer 1967, I, p. 155). Different rates of growth, taking place to a greater or lesser extent in different parts of the layer, can bring about very different morphological effects—such as ‘‘budding’’ (Abschnu¨rung), or ‘‘protrusion’’ (Hervorstu¨lpung). Baer also spoke of the ‘‘modified growth’’ which took place ‘‘in a larger or smaller part of its extension’’ (Baer 1967, II, p. 80). The difference between the individual organs in position and form is largely the result of the locally and spatially differentiated nature of this growth. Thus, for example, expansion of a section of a tube along its circumference gives rise to organs like the brain or the skull; if, on the other hand, the same tube expands along its longitudinal axis, this will result in the thinning of the layer and give rise to the formation of organs such as the oesophagus or the spinal cord (depending on the tube). Finally, if a development is restricted to a small segment of the tube a growth or protrusion occurs, as is characteristic of the spinous process (ibid.). The main factors determining the morphological structure of the final organs are therefore the location of growth and its direction, the kind of growth involved and its extent. The third form of differentiation, the histological differentiation, is the one Baer elaborates least. He merely states that it describes a differentiation within membranes. There, the texture of the tissue is formed ‘‘by cartilage, muscle and nerve mass separating, part of the mass becoming liquid and passing over into the course of the blood’’ (Baer 1967, I, p. 154). Overall, the histological differentiation organizes ‘‘the separation occurring in the embryo into manifold tissues’’ (Baer 1967, II, p. 92). Thus ‘‘the primary, the morphological and the histological differentiation repeat the same differentiations, the first above each other, the second behind each other, and the third into each other’’ (Baer 1967, II, p. 94). Although Baer analytically distinguishes three forms of differentiation, in practice they are intertwined. In particular, the differentiations do not strictly follow a temporal order. Hence, at no time do the tubes exist as completely formed structures, as the morphological or histological differentiation begins before the primary differentiation is complete (see Baer 1967, II, p. 79). Secondly, the three forms of differentiation by no means always affect the changes of the membranes as a whole. The formation of the individual organs from the tubes, especially, is locally restricted to individual segments of the membranes to be folded into tubes. Thirdly, similar structures are formed by different differentiations, so that the generation of the blood system by
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primary differentiation in the vessel layer does not imply that blood and blood vessels may not also be produced by the histological differentiation in any of the other layers. Pander had stressed that the entities subject to the folding process should not be thought of as ‘‘lifeless membranes’’ expressing ‘‘mechanically formed folds,’’ but as ‘‘of organic origin,’’ spatially differentiable due to the increase in the number of corpuscles. It would thus be wrong to compare the organic folding with that of a sheet of paper, in which ‘‘the whole sheet of paper takes part’’ (Pander 1817, p. 40). In the embryo, it is not the entire membrane that folds, but parts of it, set off by locally unequal organic growth. In the germ layer (see Baer 1967, II, p. 43) and the following layers, ‘‘the top surface develops more quickly than the bottom one, the middle part more quickly than the circumference and the front end more quickly than the rear end’’ (Baer 1967, I, p. 174). Baer thus envisions the movements that form the membranes into structures as being temporally and spatially coordinated: resembling a series of single waves, they form a complex rhythmical pattern, according to which—simultaneously and consecutively, in one or other membrane, at one or the other end or at only one point, but always choreographed as a joint ensemble—they run through the different levels and axes of the developing body, its future shape crystallizing in pulsation. For Baer, therefore, development does not just happen through repetition, but is a relation of repetitions: a ‘‘series of metamorphoses of the individual,’’ as he put it (Baer 1967, I, p. XIX).
4 Rhythmical arts The idea of rhythm as an order of organic time was part of the general tendency in the period around 1800 to conceive of nature as a rhythmical organization and hence to give a rhythmical form to representations of nature. However, discussing rhythm in this period, we must avoid the anachronistic assumption of a divide between the human sciences and the natural sciences. The claim that the episteme of rhythm around 1800 was used in various areas of knowledge and culture should not be interpreted in terms of influence and reception of ideas, for example from physiology to poetology or vice versa (for this standard view, see Hegener 1975; Mahoney 1980; Holland 2009; Mu¨ller-Sievers 2005). My argument in this paper is, rather, that rhythm designated a deeper epistemic layer. It offered an answer to the quest for a rule according to which both nature and culture (thus human beings) generate their products. In both cases, rhythm stood for the ability to keep order while at the same time enabling variation and diversity. In this sense rhythm was both an epistemological and an aesthetic category, while also making that very distinction superfluous. Perhaps surprisingly, rhythm was a relatively new concept in music theory around 1800. Even more surprising may be the fact that in music theory, as well, the new episteme of rhythm was largely a biologically inspired episteme.13 13
For a more detailed discussion of music theory and aesthetics, see Wellmann (2010).
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The single most influential music theory around the turn of the eighteenth century was probably the Akzenttheorie put forth in the work of the philosopher Johann Georg Sulzer and the two composers or music theoreticians Johann Abraham Schulz and Philipp Kirnberger. Central to the Akzenttheorie was the conceptual distinction between metre, as a mechanical measure, and rhythm, as a physiologically derived concept that related to the underlying order of both the organic world and musical movement. The Akzenttheorie conceived of music as a series of identical impulses that is varied, by accentuation, into the diversity of musical expression. Accordingly, metre represents the rigid, counted hierarchy based on the division and separation of musical length. By contrast, rhythm transforms physical movements into the movements of music. For this reason, Kirnberger argued, only the ‘‘external and, as it were, mechanical’’ nature of rhythm could be described (Kirnberger 1968, II, p. 152). Yet the special quality of rhythm was that ‘‘the ear grasped it at once’’ (Kirnberger 1968, II, p. 138). Here, Kirnberger stresses the sensual and physiological ties of rhythm that make it so direct. Despite the absence of rules, rhythm is clearly comprehensible in physiological terms. As a result of this tie to physiological disposition, rhythm has ‘‘the greatest force in music’’ (Kirnberger 1968, II, p. 142). A similar understanding of the role of rhythm can be found in aesthetic theory in general, and prosody in particular, around 1800. A paradigmatic example is the work of the German author and literary critic Karl Philipp Moritz. Moritz’s idea of the autonomous work of art was one of the salient aesthetic conceptions of the age (see Saine 1971; Schrimpf 1980; Allkemper 1990). In his Versuch einer deutschen Prosodie of 1786, Moritz applied his notion of aesthetic autonomy to language and explained how in poetry language is perfected into the work of art. In the transition from prose to poetry, that is, to the work of art, rhythm plays a constitutive role: poetry attains its independence as a work of art solely through the relational order of rhythm, which dissolves the semantic connection of the word and replaces it with the relation of syllables (see Moritz 1975). Here we see the extent to which Moritz’s concept of rhythm partakes in a wider view of the underlying order of the living world. The order of rhythm elevates language to the status of the autonomous work of art thanks to its organic qualities. Furthermore, Moritz’s concept of the autonomy of artistic productions is constructed in analogy to the autonomous order of nature. Moritz paints a picture of a permanently self-destroying and re-forming nature (Moritz 1962). Life perpetually and continuously emerges anew as individual structures are isolated from the whole and then restructured into a new context. The highest form of this kind of formation is sexual reproduction. The embryo obtains through its own ‘‘movement … its own centre of gravity and the axis of its rotation in itself’’ (Moritz 1962, p. 97). Embryonic movement is envisioned here as a dual process: first, the emergent embryo increasingly isolates itself from the mother’s body through its own bodily movements. The beginning of the embryo’s independent life is marked by the ability to move its own limbs. But independent physical movement is only the beginning of development. In a second step, organic formation means a development into ever higher forms of movement. The highest form of movement, the ultimate goal of this process, is not physical but linguistic movement
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(Sprachbewegung). From physical movement, the development stretches ‘‘to where the gentlest movement, in the true tool of language, becomes language itself’’ (Moritz 1962, p. 98). As a living creature, the embryo becomes more independent the more it is able to ‘‘speak through itself’’—first through its physical and later through its linguistic movements. The body ‘‘speaks’’ through its movement just as the moment of movement is constitutively retained in language, for ‘‘in what lives and thinks, formation, movement and sound are determined—causing the whole to dissolve again in harmony, the all-encompassing again encompassing itself’’ (Moritz 1962, p. 98). Secretion, movement and sound (Absonderung, Bewegung, Laut)—that is, according to Moritz, the triad of man’s perfection, his inner order and determination, the rhythm of his development. Moritz thus incorporates a theory of embryogenesis with a theory of language: just as embryonic life emerges by forms becoming isolated and independent of a homogeneous mass, so syllables are separated from the context of the word. Then movement creates a new context between the resulting forms. What is important here is that the course of development cannot be deduced from the single form. Instead, it is only the law of the new order that constitutes the new organism’s independence and autonomy (Autonomie und Eigengesetzlichkeit). This law of development is its rhythm, which perfects itself from the bodily movement, via the linguistic movement, up to the point of poetic art. For Moritz, as for many other of his contemporaries around 1800, the time of the development of an organism is thus not linear and chronological time, but rhythmical time. Organic time is reciprocal and irregular, and it expresses itself in constant restructuring through repetition and renewal, generation and disintegration and regularity and change. It takes shape as an autonomous entity as a result of its own structuredness—embedded in the chronological flow of time, but simultaneously separated from it. The rhythmical structure is able to bring about the infinite abundance of organic forms by linking the economy of repetition to the moment of variation. The variation of rhythm can begin at any point along a discrete sequence, which means that nature is always able to operate on the border of disorder, at the limit of disarray, even at the edge of break-up. It is the constant resetting of rhythmical order that keeps the becoming organism balanced between continuation and deviation. Thus the creative elements of the generative and formative aspects of nature are to be found not in its mere progress, but in the game of repetition, the interaction between continuity and discontinuity, rule and deviation, order and chaos. The ever new forms of becoming do not emerge without laws, but on the basis of the previous rhythmical series, which simultaneously varies them into new forms in the course of their continuation.
5 Conclusion Corpuscles that flow and solidify into forms in their movement; membranes that fold and turn into tubes; tubes that thicken or taper at points; an embryo that becomes an autonomous living organism through the movement in and of its body; and, finally, the living human who is able to transform physical motion into complex
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linguistic movements and even to elevate it to the spheres of aesthetics in poetry— around 1800, the emerging organism and organic life in general have been reconceptualised, in terms of rhythmic motion, as an uninterrupted, continuous, constantly new, but never disorderly motion. The story of the episteme of rhythm around 1800, as I have attempted to sketch it in this paper, offers a new perspective on the epistemology of embryology in particular and biology in general. I have argued that temporalization is not a sufficient answer to the question of how development was understood around 1800. Instead, the new epistemology of rhythm, simultaneously conceived in various fields of knowledge, framed the generation and formation of the living as an order of time. Rhythm was considered to be the law under which nature’s temporal dimension unfolded. Development became both rule and variation—and this is what made up its aesthetic as well as epistemological momentum.
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