THE THEORY OF ^^^-^S^aj^, 



CHEMICAL EMBRYOLOGY ^^' ^'" 



Philosophy, Embryology, and Chemistry 



The penetration of physico-chemical concepts into embryology 

 has not been entirely peaceful. "In experimental embryology", it 

 has been said, "concepts borrowed from the physical sciences do not 

 admit of calculations being made, and until they do they are not 

 really playing the same role as they do in the sciences from which 

 they have been borrowed and for which they were devised." "Nothing 

 is more clear", says another writer, "in chemistry and physics than 

 that identical results follow upon identical causes. Introduce a dis- 

 turbing element, even a small one, into your experiment, and the 

 experiment will fail. Such is not the case with the developing egg." 

 W. McDougall, too, endows the egg with good intentions. "The 

 embryo", he says, "seems to be resolved to acquire a certain form 

 and structure, and to be capable of overcoming very great obstacles 

 placed in its path. The development of the forms of organisms seems 

 to be utterly refractory to explanation by mechanical or physico- 

 chemical principles." Finally, J. A. Thomson goes farther than them 

 all, and does not hesitate to say, "It is a mere impious opinion that 

 development will one day be described in terms of mechanics". 

 Chapter iv of his Gifford Lectures illustrates the antagonistic attitude 

 to physico-chemical embryology in its most acute form. 



It can hardly be a coincidence that so many among the great 

 embryologists of the past were men of strongly philosophic minds. 

 It would be absurd to support this opinion by citing Aristotle, but 

 it holds less obviously true of William Harvey, whose book on genera- 

 tion is full of thoughts about causation, and in the cases of Ernst 

 von Baer, Ernst Haeckel, Wilhelm Roux, Hans Driesch, dArcy 

 Thompson and J. W. Jenkinson, there is no doubt about it. It is not 

 really surprising, for of all the strange things in biology surely the 

 most striking of all is the transmutation inside the developing egg, 

 when in three weeks the white and the yolk give place to che animal 

 with its tissues and organs, its batteries of enzymes and its dehcately 

 regulated endocrine system. This coming-to-be can hardly have failed 



