20 



Problems, Concepts and Their History 



were thus to come to final fruition; Spe- 

 mann's precision of thought and perform- 

 ance, and his supreme intellectual power, 

 instigated their analysis in a new way, doing 

 more than full justice to the causal analytical 

 motive of Roux. 



For if in Roux many influences converge 

 and if from him many new trends begin, and 

 if in embryology after his time as directly 

 before it, it is not always easy to follow a 

 single guiding motive, yet there stems from 

 him the single modern approach, the ex- 

 periment, and this we owe to him alone. 

 It is true, as so often, that before he was to 

 perform the experiment which was to start 

 the new trend, there had been a gradvial 

 preparation for its acceptance on the con- 

 ceptual side: biological science, like physical, 

 had finally become generally experimental- 

 ized; it was no accident that Pasteur and 

 Clavide Bernard preceded Wilhelm Roux in 

 time. But Chvm had previously performed a 

 similar experiment with as striking results 

 if not as momentous influence; and Roux not 

 only performed the experiment but general- 

 ized its significance. His ability to mobilize 

 thought around it was due to his own quali- 

 ties of mind and person. 



Driesch, in a different way than Chun, 

 represents the contrast against which the 

 contribution of Roux becomes more capable 

 of evaluation. Roux had the perspicacity to 

 appreciate that the embryo could be grappled 

 with experimentally; Driesch, though he 

 made a great experimental contribution to 

 embryology, lacked it, and was so steeped in 

 metaphysics that he finally made his option 

 for philosophy proper. 



The comparison of their interpretations of 

 what they thought a single comparable ex- 

 periment illustrates the strength and weak- 

 ness of both. Roux believed he freed one 

 blastomere in the two-celled amphibian egg 

 from the influence of another by killing the 

 latter, and thought he demonstrated thereby 

 the independent differentiation of the sur- 

 viving cell. Driesch found a single isolated 

 blastomere of the two-cell echinoderm egg 

 able to form a whole embryo and believed 

 he could prove the differentiation of a cell 

 to be dependent on its position with respect 

 to the whole. Both experiments were subject 

 to critical errors, as we now know, and for 

 both eggs both explanations are partially 

 correct and partially inadequate. 



But this was not the only issue between 

 them, nor the fundamental one. Roux inter- 

 preted the egg for the first time as a mech- 



anism mechanically analyzable by outside 

 interference; Driesch envisioned it as ruled 

 by an entelechy as spiritual as any deus ex 

 machina must be. This difference was within 

 them, and not dictated by their times. 

 Though the spirit of particular times may 

 facilitate choosing one view or the other, 

 there have been mechanists and vitalists at 

 all ages. But those differences in Roux' and 

 Driesch's interpretations were here deter- 

 mined by their own casts of mind, and the 

 fact is that Roux, by his choice, brought the 

 embryo to become experimentally attackable 

 by exact investigation. Roux set the whole 

 program for experimental embryology, and 

 this is his importance, not the fact that 

 he performed an experiment which by 1910 

 had been proved to be erroneously conceived 

 and interpreted. 



Roux' importance, however, is not only in 

 terms of presenting a method of solving 

 problems, but of setting them, and this is 

 pertinent. He could perform an experiment 

 on an embryo because he could ask a ques- 

 tion of the embryo that was experimentally 

 answerable, at least within limits. His oppo- 

 sition of differentiatio sid and diiferentiatio 

 ex alio answers the warning raised by Brooks 

 (cf. rubric heading this section) that points 

 of reference must be specified. The choice 

 between them could be made in a limited 

 way by his own method of isolation; the 

 necessity of a more crucial method to certify 

 the choice led to the development of the 

 transplantation technique by Born, Harrison 

 and Spemann. And Roux' experimental pro- 

 gram, carried to its logical outcome bv the 

 addition of the transplantation methods, in 

 a way implied by it, has led straight to the 

 modern embryology which incorporates the 

 valid features of both epigenetic and pre- 

 formationistic concepts. Every embryologist, 

 whether concerned with the development of 

 enzyme systems, or the cleavage of so-called 

 determinative eggs, or with fields and gradi- 

 ents in a regulative egg, or whatever, is still 

 concerning himself with the degree to which 

 his material at a particular moment in de- 

 velopment is answering to Roux' description 

 of diiferentiatio sui or diiferentiatio ex alio. 



Roux' own primary interest was in a the- 

 oretical and philosophical problem, that he 

 called the Causalnexus of events. But his gift 

 was that he could address his problem in 

 such a way to the embrvo that the embryo 

 reacted in what Roux believed an intelligible 

 way to laboratory interference. 



The degree of intelligibility of the reac- 



