46 HUMAN BIOLOGY 



could have arisen from variants of vegetable organisms 

 in which there was such an adjustment in their metabohsm 

 as to permit eventually the development of the animal 

 type of nutrition. 



The nucleus of the animal cell, then, harks back to that 

 of the vegetable cell when mitosis had developed and become 

 as characteristic as it is in the typical animal and vegetable 

 cells of today. The transmission of mitosis, unchanged, 

 then, through hundreds of millions of years from the time 

 when animal organisms had not yet developed, predicates 

 an incredibly long time for the primal vegetable cells to 

 develop mitosis so fixed in character as to render it invariable 

 in its characters after all that time. 



The nucleus then must be an organ which in origin 

 antedates that of the animal cell. This prompts the question 

 why it arose. The answer is not at hand, but one may refer 

 to some facts which point to a solution of it. 



The life of the protocyte must have been at first passed 

 wholly in the waters of the globe in which the salts dissolved 

 from the rock crust must have been of low concentration. 

 Into the complex of the protocyte these would diffuse, 

 and it would adjust itself to them. If any chromatin obtained, 

 it would have been unaffected by them, or, if affected, only 

 to an extent that would have produced some of the variations 

 such an originally undifferentiated organism would undergo. 

 The concentration of the salts in its habitat was, however, 

 slowly increasing as it has done ever since, till now in the 

 ocean water they amount to 3.5 per cent. This increase in 

 concentration must have begun to affect, in some degree, 

 the chromatin, rendering it uncertain in its control of the 

 metabolism of the cell and also of the transmission of 

 inherited characters. When the nucleus developed, it was, so 

 to express it, to protect the chromatin from such effects, for 

 inorganic salts are wholly absent from it although the cyto- 

 plasm of the cell, animal or vegetable, may be more or less 

 densely charged with them. 



The nucleus, on this conception of one of its functions, 

 therefore, developed when the concentration of the salts in 

 the cytoplasm had considerably increased and when it was 

 about the same as in the sea water of the period. The cyto- 



