ALIMENTARY PRINCIPLE. 117 



Proteid Alimentary Principles. Of the nitrogen-contain- 

 ing 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 

 vegetable casein from various plants. 



Albuminoid Alimentary Principles. These also contain 

 nitrogen, but cannot entirely replace the proteids as foods; 

 though a man can manage with less proteids when he has 

 some albuminoids in addition. The most important is 

 gelatine, which is yielded by the connective tissue and bones 

 of animals when cooked. On the whole the albuminoids 

 are not foods of high value, and the calfs-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 of 

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

 in various proportions in animal fats and vegetable oils; the 

 most fluid containing more olein : butter contains a pecu- 

 liar fat known as butyrin. All fats are compounds of 

 glycerine with fatty acids, and, speaking generally, any 

 such substance which is fusible at the temperature of the 

 body will be useful as a food. The stearin of beef and mut- 

 ton fats is not by itself fusible at the body temperature, but 

 is mixed in those foods with so much olein as to be melted 



What- nitrogen-containing substances form an essential article of 

 diet? Whence are they obtained? Name the most important proteid 

 foods. 



What foods besides proteids contain nitrogen? To what extent 

 can they take the place of proteids? How is gelatin obtained? Should 

 we try to build up an invalid's strength on calfs-foot jelly alone? 

 Give the reasons for your answer. 



To what group of foods do fats and oils belong? Name the more 

 important. What is their chemical composition? Why are some 

 fatty bodies not nutritious ? Give an instance. 



