FOODS. 319 



proteids, albuminoids, hydrocarbons, carbohydrates, and inor- 

 ganic bodies. 



Proteid or Albuminous Alimentary Principles. Of the 

 nitrogenous foodstuffs the most important are proteids: they 

 form an essential part of all diets, and are obtained both from 

 animals and plants. The most common and abundant are 

 myosin and syntonin, which exist in the lean of all meats; egg 

 albumen; casein, found in milk and cheese; gluten and vege- 

 table casein from various plants. 



Gelatinoid or Albuminoid Alimentary Principles. These 

 also contain nitrogen, but cannot replace the proteids entirely 

 as foods; though a man can get on with less proteids when he 

 has some albuminoids in addition. The most important is 

 gelatin, which is yielded by the white fibrous tissue of animals 

 when cooked. On the whole the gelatinoids are not foods of 

 high value, and the calf's-foot jelly and such compounds, 

 often given to invalids, have not nearly the nutritive value 

 they are commonly supposed to possess. 



Hydrocarbons (Fats and Oils). The most important are 

 stearin, palmatin, and olein, which exist in various propor- 

 tions in animal fats and vegetable oils; the more fluid contain- 

 ing more olein. Butter contains also 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. A distinction is some- 

 times made between fats proper (the adipose tissue of ani- 

 mals consisting of fatty compounds inclosed in albuminous 

 cell-walls) and oils, or fatty bodies which are not so organized. 



Carbohydrates. These are mainly of vegetable origin. 

 The most important are starch, found in nearly all vegetable 

 foods ; dextrin ; gums ; grape-sugar, called also dextrose or 

 glucose (into which starch is converted during digestion) ; and 

 cane-sugar. Sugar of milk and glycogen are alimentary prin- 

 ciples of this group, derived from animals. All of them, like 

 the fats, consist of carbon, hydrogen and oxygen; but the per- 



