No. 606] 



BIOLOGICAL ENIGMAS 



339 



The simplest hypothesis to accoimt for such reprodtiction 

 lies in the supposition that each unit can give rise to an- 

 other unit suhstantially identical with itself. 



The Weismannian theory of the constitution of the 

 germ plasm,^^ which is typical of the so-called ''corpus- 

 cular theories" of the life-process or of heredity, also de- 

 mands the existence of vital elements, each possessing 

 the power of reproduction ad infinitum. The general 

 conceptions of this theory appear to find verification, first, 

 in the facts already mentioned, and second, in the discov- 

 eries of Mendelism. The recent work of Morgan and his 

 collaborators,'^*^' moreover, reveals clearly the intimate 

 connection which exists between the corpuscular "unit 

 characters" of Mendelian heredity and the histological 

 units present in the chromosomes. Consequently, it 

 would seem to be a fairly safe generalization, or at least 

 an extremely probable hypothesis, which states that the 

 distinctive properties of cells, tissues, and species are 

 primarily determined by the nature of systems of colloidal 

 particles contained in cell-nuclei and, originally, in some 

 germ-cell nucleus. 



However, in spite of the seeming strength of the evi- 

 dence, some biologists are of the opinion that such a view 

 as this must be rejected because it paralyzes thought. 

 Consider, for example, the following quotation from 

 Child.^i 



puscular] theories do not help us in any way to solve any of the fun- 



lems beyond the reach of scientific investis^ation. ' The hypothetical 

 units are themselves orsranisms with all the essential characteristics of 

 the organisms that we know; they possess a definite constitution, they 

 grow at the expense of nutritive material, they reproduce their kind. 

 In other words, the problems of development, growth, reproduction, 

 and inheritance exist for each of them, and the assumption of their 

 existence brings us not a step nearer the solution of any of these prob- 

 lems. These theories are nothin- luoro nor loss than translations of 

 the phenomena of life as we know them into terms o\ the activity of 



39Weismann, A., "The (utiu Plasm." KiiL'lish translation, 1893. 



<o hoc. cit. 



"Child, C. M., " Senescence and Rejuvenescence," 1915, 11-12. 



