36 PHYSIOLOGICAL CHEMISTRY 



was known a few years ago. Some of these substances appear 

 to be organic compounds. Although the amounts of these ma- 

 terials of unknown constitution which are required by the 

 body are only a small fraction of a gram, still their absence 

 from the diet will cause severe disorders and ultimate death. 



The importance to the body of the individual elements ex- 

 tends much beyond the function of serving as inert building 

 stones out of which the body materials are made up. Many of 

 the chemical reactions in the body are greatly influenced or 

 .modified by certain of the elements. For example, two important 

 processes, the clotting of the blood which tends to protect a 

 wounded animal from bleeding to death, and the clotting of milk 

 in the stomach, the first step in its digestion, are dependent upon 

 the presence, among other things, of calcium, and without this 

 metal neither of these reactions can occur. 



The accompanying table gives a survey in round numbers of 

 the relative amounts of the elements present in the body. 



Carbon 17.5 



Hydrogen 10.2 



Oxygen 66 



Nitrogen 2.4 



Sulphur 0.2 



Phosphorus 0.9 



Sodium 0.3 



Potassium 0.4 



Calcium 1.6 



Magnesium 0.05 



Iron 0.005 



Chlorine 0.3 



Iodine Traces 



Fluorine Traces 



Other elements Traces 



Carbon, Hydrogen, Oxygen, Nitrogen, Sulphur and Phos- 

 phorus. Carbon has the property of forming a very large num- 

 ber of compounds with hydrogen, oxygen, and sometimes sul- 



