Methods and Techniques 



27 



will continue to help him in this respect. 

 Many other techniques, biophysical, bio- 

 chemical, immunological, and so forth, allow 

 the identification and description, if not the 

 actual visualization, of components of the 

 embryonic cell at the molecular and even 

 the submolecvilar level. 



Roux was frankly skeptical of the possi- 

 bility of reducing embryological problems to 

 the molecular level: 



Auch wenn wir von den letzten Ursachen ganz 

 absehen, so ist es doch fraglich, ob wir das von Carl 

 Ernst V. Baer gesteckte Ziel: "Die bildenden Krafte 

 des thierischen Korpers auf die allgemeinen Krafte 

 oder Lebensrichtungen des Weltganzen zuriickzu- 

 fiihren," ie erreichen werden, vorausgesetzt. dass 

 die zu Grunde liegende Auffassung iiberhaupt 

 vollkommen richtig ist (1889, cited from Ges. Abh. 

 2.-28-29). 



He preferred to approach them by investi- 

 gating, by means of interference with the 

 embryo, what he called the Causalnexus of 

 events. Causality is more suspect to the mod- 

 ern scientist, and becomes mere statistical 

 probability, but following Roux, neverthe- 

 less, the tendency is fortunately to describe 

 not simple structure but events, and specific- 

 ally a seauence of events in time. If Roux 

 believed this sequence capable of being sub- 

 ject to causal analysis, he realized also that 

 the results of any such analysis could become 

 significant only in a frame of reference de- 

 fined by the normal developing embryo, and 

 must have taken for granted that the "con- 

 trol" for an experimentally treated embryo 

 must be an undisturbed one. 



If a primary obligation of the embryolo- 

 gist, before he can evaluate an experimental 

 result, is the knowing of the normal condi- 

 tion of the embryo, the fundamental paradox 

 arises that he cannot perhaps adequately 

 know the normal without the benefit of the 

 experiment, whose whole raison d'etre can 

 surely be only that it elvicidates the normal; 

 yet he cannot interpret his experimental re- 

 sult without comparison with the normal 

 control. Leaving aside, however, for the mo- 

 ment this dilemma, the task of the embryolo- 

 gist concerned with "normal" development 

 becomes the task of describing the sequence 

 of events in time as accurately as possible in 

 terms of what he can see with the tools avail- 

 able to him, and to describe the components 

 which are acting and their manner of action 

 in as precise physical and chemical terms as 

 his instruments and techniques will allow, 

 as objectively as is possible in the light of the 

 general biological and broader philosophical 

 tenets of his times. 



A first difficulty arises in that it is virtu- 

 ally impossible to observe an embryo under 

 external conditions that do not interfere 

 with it. Fixation, staining and other chem- 

 ical treatment disturb the "normal" condi- 

 tion of the embryonic cell and alter it. 

 Suffice it to say about the living embryo, 

 withovit entering into the obvious detail, that 

 the laboratory is not its normal environ- 

 ment. Indeed, is it always possible to define, 

 let alone reproduce, a "normal" environ- 

 ment? 



What is the "normal" environment of a 

 developing Bonellia or Crepidula, whose sex- 

 ual differentiation may be modified by it, 

 in terms of distance from another Bonellia or 

 Crepidula (Herbst, '36, '37; Baltzer, '37; Coe, 

 '48)? What is the "normal" salinity for the 

 development of Artemia whose form de- 

 pends on the salt concentration of its en- 

 vironment (Abonyi, '15)? To come to the 

 vertebrate, which we are in the habit of con- 

 sidering more conventional and stable em- 

 bryological material, Fundulus heteroclitus 

 embryos raised at constant temperatures 

 reach specific morphological stages after dif- 

 ferent periods of time when raised at varying 

 salinities (Merriman, unpublished). The 

 adults live and breed both in brackish water 

 and sea water in nature, and the tempera- 

 tures of the seas and the estuaries are incon- 

 stant. What then is the "normal" environ- 

 ment of the developing Fundulus? What are 

 the criteria for determining objectively 

 which set of conditions is "optimum" for 

 the embryo developing in the laboratory, 

 and what biological significance these have 

 for the organism developing in nature? 



Comparable problems arise for the chem- 

 ical embryologist who tries to describe the 

 constituent systems of the embryonic cell in 

 biochemical terms. Unpublished data of 

 Dumm have suggested that the cholines- 

 terase level of Fundulus embryos at particu- 

 lar morphological stages varies according to 

 the temperature at which the embryos have 

 been raised; and Boell (unpublished) also 

 has data suggesting that the course of enzyme 

 development in the amphibian can be altered 

 by varying the temperatures at which the 

 embrvos are reared. Weiss ('49) has intro- 

 duced in another connection a useful con- 

 cept of "molecular ecology" which may well 

 serve to remind the embryologist of what 

 he already knows but sometimes forgets, 

 namely, that the embryo has an internal as 

 well as an external environment that may 

 well bear more strict definition than it has 

 always hitherto received. 



