GENETICS 99 



stand by this that the cytoplasm alone is respon- 

 sible? Is it possible that the genes, once having 

 done their part in bringing the character to ex- 

 pression, have ceased to act? That they have 

 provided the cytoplasm with a degree and kind of 

 development which enables it to act alone during 

 the remainder of its life? The evidence is distinctly 

 against such an interpretation. Cells may lose 

 their nuclei and thereafter exist as cytoplasmic 

 units, but they are relatively short-lived and their 

 activities are little more than chemical reactions 

 of their specific contents. The one common ex- 

 ample of this phenomenon, the erythrocytes of 

 mammalian blood, is a convincing demonstration 

 of this fact. Experiments with artificial enuclea- 

 tion also indicate a lack of anabolic power in cyto- 

 plasm isolated from its nucleus. Since individual 

 adaptive responses are often anabolic, we may 

 conclude without hesitation that the nucleus re- 

 mains active throughout the life of the cell, and 

 consequently that its essential elements, the chro- 

 mosomes and genes, are also active. 



It is true, of course, that the literature of genetics 

 deals merely with the production of characters, 

 not with their behavior during the life of the in- 

 dividual. Genes are handed down from generation 

 to generation, and a character is heritable if its 

 genes normally result in its appearance during 

 embryonic or postembryonic life. We cannot say 



