16 STUDIES IN PHYSIOLOGY 



3. THE CHEMICAL COMPOSITION OF THE HUMAN BODY 



We are now to consider the application of some of these 

 principles of chemistry to the study of the human body. 

 Chemists have accurately determined the chemical composi- 

 tion of the various parts of the body, and we will discuss 

 some of the most important substances that have been 

 shown by analysis to be present. 



Water. The great importance of water in the composi- 

 tion of living substance is evident from the fact that it 

 'forms about 62% of the weight of an adult man. Hence, if 

 all the water were removed from the body of a man weighing 

 one hundred and sixty-five pounds, the solids that remained 

 would weigh but a little over sixty pounds. The different 

 organs vary greatly in their percentage of water : bones con- 

 tain about 22%, muscles have 75%, and the kidneys 82 %. 



Mineral Matters. Mineral matters are found in greatest 

 quantity in the bones. When we burn bones, about one 

 third of the weight disappears, the remaining two thirds 

 being bone ash, which is the mineral matter. Every part of 

 the body, however, contains some mineral ingredients, for 

 when muscle, liver, brain, or blood is burned, in each case 

 there remain some traces of ash. 



Gases. A large amount of the gas oxygen is taken into 

 the lungs, whence it is distributed to all the organs by the 

 blood. We shall find that in our bodies, as well as in 

 the experiments with the match this oxygen performs the 

 all-important function of causing oxidation. One of the 

 products of this oxidation is the gas we have already con- 

 sidered ; namely, carbon dioxid. If we blow through a tube 

 or a straw into a glass of clear limewater, the liquid be- 

 comes milky. Our breath is therefore constantly removing 

 from our bodies a gas exactly like one of those formed by 

 burning the match. 



Fats. The amount of fat in the body varies greatly in 



