CHEMIC COMPOSITION OF THE HUMAN BODY. 37 



INORGANIC CONSTITUENTS. 



The inorganic compounds and mineral constituents obtained 

 from the solids and fluids of the body are very numerous, and, in 

 some instances, quite abundant. Though many of the compounds 

 thus obtained are undoubtedly derivatives of the tissues and necessary 

 to their physical and physiologic activity, others, in all probability, 

 are decomposition products, or transitory constituents introduced 

 with the food. Of the inorganic compounds, the following are the 

 most important: 



WATER. 



Water is the most important of the inorganic constituents, as it 

 is indispensable to life. It is present in all the tissues and fluids 

 without exception, varying from 99 per cent, in the saliva to 80 

 per cent, in the blood, 75 per cent, in the muscles to 2 per cent, in 

 the enamel of the teeth. The total quantity contained in a body 

 weighing 75 kilograms (165 pounds) is 52.5 kilograms (115 pounds). 

 Much of the water exists in a free condition, and forms the chief part 

 of the fluids, giving to them their characteristic degree of fluidity. 

 Possessing the capability of holding in solution a large number of 

 inorganic as well as some organic compounds, and being at the same 

 time diffusible, it renders an interchange of materials between all 

 portions of the body possible. It aids in the absorption of new 

 material into the blood and tissues, and at the same time it transfers 

 waste products from the tissues to the blood, from which they are 

 finally eliminated, along with the water in which they are dissolved. 

 A portion of the water is chemically combined with other tissue con- 

 stituents and gives to the tissues their characteristic physical properties. 

 The consistency, elasticity, and pliability are, to a -large extent, con- 

 ditioned by the amount of water they contain. The total quantity 

 of water eliminated by the kidneys, lungs, and skin amounts to about 

 3 kilograms (6| pounds). 



CALCIUM COMPOUNDS. 



Calcium phosphate, Ca 3 (PO 4 ) 2 , has a very extensive distribu- 

 tion throughout the body. It exists largely in the bones, teeth, and 

 to a slight extent in cartilage, blood, and other tissues. Milk con- 

 tains 0.27 per cent. The solidity of the bones and teeth is almost 

 entirely due to the presence of this salt, and is, therefore, to be 

 regarded as necessary to their structure. It enters into chemic union 

 with the organic matter, as shown by the fact that it can not be 

 separated from it except by chemic means, such as hydrochloric 

 acid. Though insoluble in water, it is held in solution in the blood 

 and milk by the proteid constituents, and in the urine by the acid 



