CHAPTER III. 

 THE CRITERIA OF LIFE. 



Laying aside, for the present, all speculation as to the 

 connecting links between the matter that we call living, 

 and that which we declare to be not living, it becomes 

 necessary to establish certain criteria by which .the 

 former be recognized. These distinctive properties have 

 been formulated by Huxley as follows: 



1. Its chemical composition. 



The chemical composition of living substance is based 

 upon a complex combination of O, H, N, and C known 

 as protoplasm. It is a protein that is entirely unknown 

 except as a product of living substance. Its exact com- 

 position is not determined because it is scarcely possible 

 to study it apart from other elements by which and 

 through which many of its functions are carried on. 

 Chief among these are S and P. 



2. 72s universal disintegration and waste by oxidation; */ a 

 and its concomitant reintegration by the intussusception jj^ 

 of new matter. 



Life is accompanied by the manifestation of energy 

 which implies combustion by oxidation, chemical 

 disintegration of the complexly organized protoplasm, 

 and its reduction into more highly oxidized but simple 

 compounds, such as carbonic oxide and water. This 

 would soon result in complete destruction of the proto- 

 plasm by analysis were it not within the power of the 

 living substance to make good this loss as rapidly as it 

 occurs. 



When the living substance is young, the function of 

 synthesis takes precedence over analysis and the organ- 

 ism is said to grow. This growth is, however, entirely 



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