96 THE HUMAN MECHANISM 



the carbohydrates they are compounds of carbon, hydrogen, 

 and oxygen, although the oxygen is always present in small 

 quantities. The formula for one of the fats is C 51 H 98 O 6 , and 

 this composition is typical of all of them. 



Fats may be split up into certain acids (fatty acids) and 

 glycerin, and when treated with alkalies, like caustic soda or 

 caustic potash, they form soaps. They are insoluble in water. 

 Like the carbohydrates they contain no nitrogen. 



8. Oxidizable and nonoxidizable nutrients. All the above 

 nutrients may and do combine with oxygen within the cells 

 of the body, although the way in which this chemical union is 

 brought about is one of the unsolved problems of physiology. 

 While all the nutrients may be burned after being dried, 

 such combustion requires a high temperature. Within the 

 body they are not only burned (that is, combined with oxy- 

 gen) at a temperature rarely exceeding 39 C. (100 F.), but 

 they undergo oxidation while in a moist state or even in 

 solution. However this oxidation may be effected within the 

 cell, there can be no doubt that it yields the heat for keeping 

 the body warm and possibly the power for its work. 



The remaining groups of nutrients the inorganic salts 

 and water are, for the most part, not oxidized in the body. 



9. The groups of inorganic salts and water. These nutrients 

 are absolutely necessary for the proper nourishment of the 

 body, their presence in the blood and lymph and in the liv- 

 ing cells being indispensable to the processes of life. The 

 salts are taken in small quantities, partly as salt itself, partly 

 as portions of the various foods we eat. During growth they 

 furnish much of the mineral matter of bones, and since the 

 body is daily losing salt, it is necessary that salt be supplied 

 in the food. Salts, however, are not acted on to any large 

 extent in the alimentary canal by the processes of digestion; 

 they are largely absorbed in the same form as eaten. Hence 

 they do not concern us at present to the same extent as do the 

 oxidizable nutrients, which generally have to be chemically 



