14 BIOLOGY 



been evolved from " inorganic " substances, then we 

 shall find that what we at present consider inorganic 

 is in reality organic matter. 



CHAPTER II 



THE CRITERIA OF LIFE 



IF we lay aside all speculation as to the origin of Life, 

 and consider the world around us, we are able to place 

 most of the things we see under one of two categories, 

 the living and the dead. The very fact that we group 

 things under these headings makes it necessary for us 

 to be clear as to what we mean by living and non-living, 

 or, in other words, to lay down some criteria by which 

 the living may be distinguished from the non-living. 

 As a fairly satisfactory and quite workable set of criteria, 

 we may take the three properties laid down by Huxley 

 as distinctive, or peculiar to living matter. 



1. Its chemical composition. 



It is a protein practically unknown except as a pro- 

 duct of living substance. No one as yet has been able 

 to give its exact composition, as it is impossible to study 

 it apart from other elements which may aid it only in 

 carrying out certain of its functions. This much may 

 be said that it is a highly complex combination of 

 Oxygen, Hydrogen, Carbon, and Nitrogen, and is known 

 as protoplasm. 



2. Its universal disintegration and waste by oxida- 

 tion, and its concomitant reintegration by intussus- 

 ception. 



