OUR FUTURE COURSE 207 



alone is incapable of continued constructive ac- 

 tion; everything that it accomplishes is ultimately 

 referable to the controlling action of the chromo- 

 somes. Two interpretations of the activity of the 

 chromosomes in the development of acquired char- 

 acters are possible: We may conclude that they 

 always exert the same influence and that the cyto- 

 plasmic result is cumulative, or that the chromo- 

 somes also undergo a cumulative change which is 

 responsible for the condition of the cytoplasm, 

 that the ultimate expression of the acquired char- 

 acter is the result of an actual increase, through 

 use, of the functional capacity of the genes involved 

 in its production. It must be admitted that these 

 interpretations are speculative, but the probability 

 of the latter is attractive. There is nothing to show 

 that increased muscular power is purely a result 

 of quantitative modification of cytoplasm or that 

 tolerance for morphine is due to the accumulation 

 in the cells of the body of some product which aids 

 in protecting it against the drug. Again exact 

 information is to be desired, and in its absence 

 we must fall back on a logical interpretation of the 

 available facts. It is commonly known that the 

 material of which the body is composed undergoes 

 frequent renewal under the control of nuclear 

 activity.^ This fact seems much more compatible 

 with the idea of gradual modification of the func- 



4 McClung, C. E., Cowdry's General Cytology, pp. 665-667, 1924. 



