300 THE HUMAN BOD*. 



Hydrocarbons (Fats and Oils). The most important 

 are stearin, palmatin, margarin, and olein, which exist in 

 various proportions in animal fats and vegetable oils; the 

 more fluid containing most olein. Butter contains a 

 little of a fat named butyrin. Fats are compounds of 

 glycerine and fatty acids, and any such substance which 

 is fusible at the temperature of the Body will serve 

 as a food. The stearin of beef and mutton fats is not 

 by itself fusible at the body temperature, but is mixed 

 in those foods with so much olein as to be melted in the 

 alimentary canal. Beeswax, on the other hand, is a fatty 

 body which will not melt in the intestines and so passes on 

 unabsorbed; although from its composition it would be 

 useful as a food could it be digested. It is convenient to- 

 distinguish fats proper (the adipose tissue of animals 

 consisting of fatty compounds inclosed in albuminous cell- 

 walls) from oils., or fatty bodies which are not so surrounded. 



Carbohydrates. These are mainly of vegetable origin. 

 The most important are starch, found in nearly all vege- 

 table foods; dextrin; gums; grape sugar (into which starch 

 is converted during digestion); and cane sugar. Sugar of 

 milk and glycogen are alimentary principles of this group, 

 derived from animals. All of them, like the fats, consist 

 of carbon, hydrogen and oxygen; but the percentage of 

 oxygen in them is much higher, there being one atom of 

 oxygen for every two of hydrogen in their molecule. 



Inorganic Foods. Water; common salt; and the chlo- 

 rides, phosphates, and sulphates of potassium, magnesium 

 and calcium. More or less of these bodies, or the materials 

 for their formation, exists in all ordinary articles of diet 

 so that we do not swallow them in a separate form. Phos- 

 phates, for example, exisj; in nearly all animal and vegetable 

 foods; while other foods, as casein, contain phosphorus in 

 combinations which in the Body yield it up to be oxidized 

 to form phosphoric acid. The same is true of sulphates, 

 which are partially swallowed as such in various articles of 

 diet, and are partly formed in the Body by the oxidation of 

 1 the sulphur of various proteids. Calcium salts are abun- 

 f dant in bread, and are also found in many drinking waters. 



