462 GENERAL CONSIDERATIONS 



During adolescence the adverse effects of departures from the normal are 

 minimized or overcome ; during senescence such effects tend to remain and 

 to be accentuated. The curve of a normal life cycle possesses a certain 

 symmetry; its span varies and is a part of the inheritance of the individual 

 (Fig. 14). Normal living throughout life conduces to the fullest realiza- 

 tion of this inheritance; departures from such living tend to shorten the 

 cycle. Theoretically, senescence should be a period as normal and accom- 

 panied by as perfect health as is either of the previous periods. 



468. Organismal Concept.^The concept of the organism as a unit 

 may be contrasted with the cell concept. The cell is the morphological 

 unit, some organisms existing as single cells, others as many. In the first 

 case all functions necessary to life are performed by the one cell; in the 

 second these functions are apportioned to the different cells that make 

 up the whole, and the individual cells become dependent upon their 

 association for continued existence. Applying the organismal concept 

 to a protozoan, it is seen to be comparable not to any one cell of a meta- 

 zoan but to the whole metazoan body. It is, from a physiological stand- 

 point, correspondingly complex. 



The many-celled organism has possibilities greater than the sum 

 total of the possibilities possessed by the cells taken one by one or even 

 in groups. These larger activities are the result of interaction between 

 cells. Thus such an organism is comparable to a community made up of 

 individuals, having peculiar powers and activities which belong to it 

 as an organized whole and capacities which it possesses by virtue of its 

 organization. 



