52 WHAT IS LIFE 



sary to life, was shown by Lavoisier about one hun- 

 dred and fifty years ago, but — as W. Mansfield Clark 

 recently said — "what happens in the cell itself when 

 oxygen is brought to it is as much a mystery as ever." 



Salts play a large role in life phenomena. Thus, 

 blood contains sodium chlorid and other salts. 



From sixty -five to eighty per cent of the organism 

 consists of hydrogen and oxygen in the form of 

 water. According to Martin Mendelsohn, of the Uni- 

 versity of Berlin, the enormous stream of fluid sub- 

 stances that circulates through the body is kept in 

 motion by the action of the cells and glands, with the 

 heart "only a subsidiary organ of the circulation 

 system — an unusually large blood vessel." 



All the elements found in organisms are enumer- 

 ated on pages 100 and 101. Carbon is present in 

 all organic compounds, and organic chemistry is de- 

 scribed as the chemistry of carbon. 



Compounds that consist of hydrogen and carbon 

 only, the hydrocarbons, are classed in two main 

 divisions, the open-chain (aliphatic, including the 

 organic fats) compounds, and the closed ring, or 

 cyclic, compounds. These two types of the chemical 

 structure of hydrocarbons also are the basis of the 

 classification of all organic compounds. For it is 

 held that all other organic compounds may be de- 

 rived from hydrocarbons by the replacement of 



