194 ELEMENTS OF PHYSIOLOGY 



by increase of the bodily heat. It was learned that fat 

 is stored up in the interior of cells (Fig. 38). Sugar can 

 be changed into fat by the cells and stored away for future 

 use in producing heat and motion. Thus sugars and 

 starches, or the carbohydrate class of foods, have three uses. 

 Knowing the great importance of movement to our life, 

 and also the fact that the body is constantly losing heat, 

 day and night, winter and summer, the importance of this 

 class of foods is easily understood. Some animals and 

 plants have fat and oils or liquid fat in their tissues .ready 

 for use as food by man. This gives us a third class 

 of foods, the 



333. Fats. Fats are exactly the same in function as 

 the carbohydrates. A pound of fat in oxidizing gives 

 out two and one half times as much heat as a pound 

 of sugar or starch, and about the same as a pound of 

 albumin. It may be stored up as fat in the body if not 

 oxidized in the muscles to promote heat and work. Under 

 all circumstances, a certain amount of nitrogenous or 

 proteid food is required by the muscular tissue, for, as 

 in all cells, the real living framework of the muscular 

 fibers contains albuminous substances as one of its essen- 

 tial constituents. We may, then, think of fat and sugar 

 as having the same relation to the structural substance 

 of the muscle as the coal has to the structural parts of 

 the engine. 



334. Mineral Foods. The food stuffs so far mentioned 

 are all organic substances. There are many inorganic or 

 mineral food stuffs, such as carbonate of lime, phosphate 

 of lime, iron, and sulphur that are necessary to the body, 

 yet we cannot get them directly from mineral sources. 

 The bones are largely made of lime, and if we could 

 assimilate lime by eating it, or drinking it in " hard " water, 

 then the people who live in limestone regions and drink 

 hard water might all be giants. We can get phosphates 



