PROTEIN. 233 



forming a clear solution ; and if an acid is added to 

 this, so as to neutralize the alkali, a precipitate falls, 

 which is precisely the same from whichever of these 

 three substances it is obtained ; to this precipitate the 

 name of protein is given. Protein consists of oxygen, 

 hydrogen, carbon, and nitrogen, like the substances 

 from which it is obtained ; but it contains no sulphur 

 or phosphorus, whilst they always contain a small 

 quantity. 



600. The knowledge of this fact, that the fibrin 

 and albumen, &c., of plants, are identical in compo- 

 sition with some of the most common forms of animal 

 matter, throws great light on the nutrition of animals. 

 It shows that the gluten and albumen of plants used 

 as food, may immediately enter into the system of 

 the animal ; whilst gum, starch, sugar, &c., must 

 undergo a change, before they can constitute a part 

 of the body of an animal. 



601. It has already been stated that vegetable 

 and animal oils consist of the same three elements ; 

 many of these oils contain precisely the same pro- 

 portions of carbon, oxygen, and hydrogen : hence 

 by some chemists it has been supposed, that the oil 

 which exists in those vegetables used as food, might 

 contribute directly to the formation of fat, without 

 undergoing any change ; though, on the other hand, 

 many facts might be quoted to show that this view 

 is improbable; and that the fat of animals is formed 

 from starch, gum, and sugar, by a kind of fermenta- 



20* 



