No.533] NUCLEUS AND CYTOPLASM IN HEREDITY 293 



have been taken from the body under perfectly aseptic 

 conditions and kept suitably warm and moist. 



There is no obstacle in the way of supposing, further- 

 more, that if we regard ferments as of nuclear origin, 

 the cytoplasm of a given tissue may not modify the fer- 

 ment, as it itself takes on the necessary modifications 

 for its own specific functions. We have good evidence 

 that the production of ferments can be modi lied by even 

 the substratum on which living organisms grow, and 

 such a relation as this, close as it is, is certainly less inti- 

 mate than that existing between nucleus and cytoplasm. 

 For example, molds cultivated upon starch form dia- 

 stase, but if provided with albumin they will produce in- 

 stead a proteolytic ferment. Moreover, by gradually 

 altering their other nutriments, yeasts can be made to 

 utilize after a time various foreign compounds. 



But granted the necessity of some such set of con- 

 trollers as the enzymes, and locating them in the chromo- 

 somes of the germ-cells, does this not commit us to n 

 ri.u-idly chromosomal theory of heredity ! By no means. 

 If, as all evidence indicates, ferments operate as cata- 

 lyzers, then we must not forget that it is the very gen- 

 eral belief among chemists that catalytic agents do not 

 initiate the chemical reactions with which we find them 

 associated, but that they only tremendously accelerate 

 such reactions, or in a few known instances retard them. 

 Since the nature of the building material must determine 

 fundamentally the nature of the thing built, we must 

 look outside the enzymes for much that will determine 

 the peculiar individual outcome of the developmental 

 processes. Leaving out of consideration for the present 

 other functions the chromosomes may subserve, we 

 might regard them as a sort of gauge for the feeding out 

 of enzymes at the proper rate to bring about proper 

 velocity reactions in the other cellular constituents, and 

 perhaps regard the whole matter of mitosis and exact- 

 ness in chromosomal distribution as a mechanism by 

 which a quantitative metabolic regulation is maintained. 



But because chromosomal influences can regulate the 



