260 



PHYSIOLOGICAL 0ENETIC8 



catalyzers. As enzymes are extremely specific, their action 

 requires t h«- proper substratum; to which might be added the 

 optimum conditions in acidity, in regard to coferments, in the 

 relations of enzyme and carrier substance, in colloidal and 

 viscosity conditions of the medium. When all these conditions 

 are properly provided, the action of the enzyme (which might 

 always have I >< «ii present since fertilization, though perhaps not 

 in sufficient concentration) may begin, and this we call now the 



Gene A 

 Gene B 

 Gene C 



CADI ChDM Ch.D.m 



B A C 



Fig. 54. — Diagrammatic representation of the activation of the gene by proper 

 cytoplasm. {From Goldschmidt, 1927, Phys. Ther. d. Vererbg.) 



activation of the gene. It was shown in the chapter on develop- 

 mental mechanics that development, from the standpoint of the 

 whole embryo, i.e., the cytoplasm, consists in a series of "stratifi- 

 cations" of cytoplasmic differences initiated by a gene-controlled 

 process. Thus, one substratum is transformed into two or more 

 different ones, which now can provide the proper substratum for 

 the action of new genes. We may thus describe the activation 

 of the genes in terms of the accompanying diagram (Fig. 54). 

 We assume three genes A, B, C which, or the products of which, 

 are ready for action as soon as the proper substratum is provided. 

 At a stage of development, Ch. DI, a cytoplasmic segregation 

 into two different substrata occurs. The lower one is the proper 

 basis for the action of gene B, and the chain of reactions controlled 

 by this gene is set in motion. At the stage Ch DII, the stratifica- 

 tion has produced five areas, the topmost of which is the proper 

 substratum for the gene A. The third stratification provides 

 the substratum for C. The actual facts may be much more 

 complicated, but it is most probable that the general relations 



