148 Life and Death, Heredity and Evolution 



Hertwig has developed later a general theory of mating, 

 rejuvenescence and kindred matters; a theory which is at 

 once extremely special and extremely indefinite. It is based 

 upon ideas of a necessary proportion in quantity between the 

 mass of the nucleus and that of the cytoplasm. As growth 

 occurs the cytoplasm increases faster than the nucleus, so 

 that after a time the nucleus is too small in proportion to the 

 amount of cytoplasm. This brings about in some way a sud- 

 den increase in the growth of the nucleus, and this in turn 

 causes division of the cell. In the course of many cell 

 generations, through irregularities in division, and through 

 the action of various agents, the nucleus may become too 

 large in proportion to the cytoplasm. Enlargement of the 

 nucleus has been found to occur in cold; in hunger; when 

 the animals are overfed; and in various other conditions. 

 In such conditions the animals do not divide frequently, 

 and this is attributed by Hertwig's theory to the dispropor- 

 tionate size of the nuclei. Such conditions of large nuclei 

 and slow reproduction, with other pathological symptoms, 

 are spoken of as states of "depression." Such depression 

 can be remedied, if it has not gone too far, in various ways, 

 by change of temperature, of food, and the like ; the essen- 

 tial thing that then happens, according to this view, is that 

 the nucleus reduces its size, by throwing out substance into 

 the cytoplasm, or otherwise. But if depression has gone 

 too far for this, it can be overcome only by a deep-seated 

 reorganization of the nucleus. Such a deep-seated reor- 

 ganization occurs in the processes connected with mating; 

 hence, it is held, these processes restore the normal balance 

 of nucleus and cytoplasm ; the depression disappears, and 

 the organisms continue to live and multiply. 



Such a theory appears artificial and based upon super- 

 ficial features. When one considers the complex chemical 



