Chromatin as ''Hereditary Suhstnnee'' 341 



Although some investigators report having failed to get 

 tlie differential reaction deseril)ed by Lillle, on the wlioli' his 

 evidence with much more of like purport that might \)v cited, 

 makes tlie conclusion seem unesca])ahlc that for a consider- 

 able range of animals the ''nucleus plays an essential part in 

 pigment formation by some activity which great Iv resembles 

 an oxidizing action." 



How far the chromosomes are responsible for this activity, 

 is by no means settled. Hooker could find nothing similar 

 to von Szily\s "pigment bearers", or evidence of any kind 

 that the melanin granules come from chromatin. Indeed, he 

 brings forward a number of weighty considerations against 

 the theory that in the frog at least the chromatin Is directly 

 concerned in pigment production. He holds that his obser- 

 vations demonstrate that in this animal "melanin is formed 

 in the cytoplasm of the cell at the point of known greatest 

 efficiency of the nucleus as an oxidizing agent." 



Summarizing our examination of the direct ezidence fa- 

 vorable to the theory of chromosomes, or at least chromatin, 

 as the mechcmism of heredity, we find that in the oricfin and 

 grozvth of flagella and pigment in some organisms the tJieory 

 receives a certain amount of support. 



B. INDIRECT EVIDENCE 



The Indirect evidence favorable to tlie tlieory will now be 

 considered. Significantly enough the theory is supporti'd 

 chiefly by this sort of evidence. To such an extent is this 

 true, and so sterling in quality and great in quantity is the 



a mixture of one of the naphthols with a derivative of one of the ben- 

 zenes. This mixture ])roduc'es a deej) vioh't-cohu-cd fluid on oxidation. 

 By treating kidney tissue, for exanii)le, under projjer conditions witli 

 this indicator, IJllie found that the "nucleus of tiie tui)ule cells remains 

 comparatively clear and uncolored, and that the coloration of the cyto- 

 plasm is diffuse, but lypicallij deeper in (he 'unmedhile mitihhorhood of 

 the nucleus than elsewhere— n clear indication that oxidations arc espe- 

 cially active at the nuclear surface." 



