6 HUMAN PHYSIOLOGY 



appear in an almost pure form, they are physiologically more 

 simple, but for this reason also less independent, than unicel- 

 lular individuals. 



All organisms composed of many physiologically different 

 cells develop from undifferentiated cells. The physiological 

 differentiation is accompanied by a morphological differen- 

 tiation, which is expressed in the various forms of the cells. 



Although, in consequence of the division of labor, the 

 various kinds of cells have different functions, yet those 

 physiological processes which are connected with the char- 

 acteristic constituents of all cells must be common to all 

 kinds of cells. These physiological processes include in 

 general the processes which belong to the nourishment and 

 reproduction of the cells. These processes are governed by 

 the nucleus. The nucleus of the reproductive cells is the 

 bearer of the inheritable qualities of the organism. 



The separation of the living substance into nucleus and 

 protoplasm is the morphological expression of the physio- 

 logical division of labor, the nucleus being predominantly 

 concerned with the nourishment and reproduction, while the 

 protoplasm chiefly reacts upon external influences. 



3. GROWTH AND DEATH. ORIGIN AND DEVELOP- 

 MENT OF THE LIVING BEING 



If in a living being assimilation and the addition of assimi- 

 lated products predominate over dissimilation, growth of the 

 organism results; if dissimilation predominates, the body 

 decreases. In each organism the assimilation predominates 

 at first, the body grows ; later on the activity of assimilation 

 decreases, the body begins to decrease, and this results in 

 physiological death or in death brought on by senile decay. 



A new living being originates only by the growing and 

 the developing of a part separated from an already existing 

 living body. This part grows and develops into a new living 

 being either alone or after the union with a part of a second 

 organism of the same kind. Life propagates itself from the 

 mother- to the daughter-organism. 



