30 



THE AMERICAN NATURALIST 



[Vol. L 



substances, each owing its characteristic properties to a 

 definite molecular composition, can produce a living indi- 

 vidual in which specific peculiarities are associated with 

 matter in a state of flux. But it is altogether outside the 

 scope and aim of this address to discuss whether the boun- 

 dary between biochemistry and biology can be bridged 

 over, and if so, in what way. I merely wish to emphasize 

 strongly that if a biologist wishes to deal with a purely 

 biological problem, such as evolution or heredity, for 

 example, in a concrete and objective manner, he must do 

 so in terms of living specific individual units. It is for 

 that reason that I shall speak, not of the chromatin-sub- 

 stance, but of chromatinic elements, particles or units, and 

 I hope that I shall make clear the importance of this dis- 

 tinction. 



To return now to our chromatin ; I regard the chroma- 

 tinic elements as being those constituents which are of 

 primary importance in the life and evolution of living or- 

 ganisms mainly for the following reasons: the experi- 

 mental evidence of the preponderating physiological role 

 played by the nucleus in the life of the cell ; the extraordi- 

 nary individualization of the chromatin particles seen uni- 

 versally in living organisms, and manifested to a degree 

 which raises the chromatinic units to the rank of living 

 individuals exhibiting specific behavior, rather than that 

 of mere substances responsible for certain chemico-phys- 

 ical reactions in the life of the organism ; and last, but by 

 no means least, the permanence and, if I may use the term, 

 the immortality of the chromatinic particles in the life- 

 cycle of organisms generally. I will now deal with these 

 points in order ; my arguments relate, in the first instance, 

 to those organisms in which the presence of true cell-nuclei 

 renders the identification of the chromatin-elements cer- 

 tain, as pointed out above, but if the arguments are valid 

 in such cases they are almost certainly applicable also to 

 those simpler types of organisms in which the identifica- 

 tion of chromatin rests on a less secure foundation. 



The results obtained by physiological experiments with 



