CHAPTER IV 



GENERAL PECULIARITIES OF PROTOPLASM AS 

 A PHYSICAL SYSTEM 



In considering the general peculiarities of living proto- 

 plasm, it is essential to recognize that its characteristic 

 properties and activities depend upon features of composi- 

 tion and structure which are kept in permanent existence 

 only through a continued process of compensation, 

 consisting in the metabolic construction of new and 

 specific compounds to replace those broken down or lost 

 in vital activity. Without this continual automatic 

 renewal and repair the system is an unstable one and 

 cannot persist. Physical diffusion and the normal 

 chemical processes of oxidation and hydrolysis all act 

 toward producing a disintegration of the system; these 

 effects are well seen in experiments on autolysis; the 

 dead cell digests itself and its soluble constituents diffuse 

 into the surroundings. During life the structural and 

 chemical integrity of the system is maintained by means 

 of its continued synthetic activity; the cessation of this 

 activity is the essential change in death. 



This general conception of living matter, as a system 

 which holds its own through a balance of constructive 

 and disintegrative processes, is fundamental in physi- 

 ology. Other systems exhibiting an analogous type of 

 equilibrium, i.e., between constitutive and disintegrative 

 processes, are of frequent occurrence in nature, and have 

 been classed by Ostwald as "stationary systems.'" 



^ Ostwald, Vorlesungen iiher Natiirphilosophie, Leipzig (1902), 

 chaps, xii, xv. 



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