52 ELEMENTS OF PHYSIOLOGY 



to separate the carbon from the oxygen. Thus we see how 

 animals and plants help each other, and how all nature 

 forms one harmonious whole (Fig. 24). 



84. List of Substances. The most important solid and 

 liquid substances of which the body is composed are water, 

 albumin, fat, sugar, salt, lime, soda, potash. Water, salt, 

 and lime 'do not oxidize, either in or out of the body. 

 Their use in the body is more mechanical than chemical. 



One ounce of albumin is completely oxidized by one and one half 



ounces of oxygen. 



One ounce of fat is completely oxidized by three ounces of oxygen. 

 One ounce of sugar is completely oxidized by one and one fifth ounces 



of oxygen. 



85. Water. Water does not oxidize. It is composed of 

 two gases firmly united : hydrogen and oxygen ; that is, 

 water is hydrogen already oxidized. Water forms three 

 fourths of the body. When a solid substance is dissolved 

 in a liquid so that each remains unchanged in its essential 

 properties, the result is a solution of the solid in the liquid. 

 Sugar in water is sugar still ; in fact we can taste sugar 

 only when it is dissolved. Most solutions can go any- 

 where that water alone can go. In the stomach the food 

 is dissolved and taken into the circulation. The blood 

 containing the food in solution penetrates to the cells, 

 carrying nourishment and washing away the waste mate- 

 rial. By means of the perspiration, water takes heat from 

 the body. About three quarts of water are taken into the 

 body each day, either alone or in watery foods. 



86. Albumin (Proteid). We learned that protoplasm, or 

 living matter, differs from inorganic matter in containing an 

 albuminous material, composed partly of nitrogen. The 

 other two oxidizable foods, fat and sugar, do not contain 

 nitrogen. Pure nitrogen is found in the air, but the body 

 cannot use it in that form, for nitrogen is very inactive when 

 pure ; when compounded in albumin, however, it gives to 



