Classification of Feeding Principles. 5 



together into two classes. The first class includes constituents 

 rich in nitrogen, or nitrogenized matters ; and the second, con- 

 stituents free from nitrogen, or non-nitrogenized compounds. To 

 the former, the nitrogenized compounds, belong: 



Vegetable albumen, a substance identical in composition 

 with the white of egg. 



Gluten or vegetable fibrin, a compound occurring in con- 

 siderable quantity in wheat, and giving elasticity to the 

 dough made with wh eaten flour. 



Vegetable casein, a substance identical in composition with 

 the curd of inilk. 



Legumin, a peculiar vegetable principle, which derives 

 its name from its occurrence in large quantity in peas, 

 beans, and other leguminous seeds. 



A few other nitrogenized compounds of rarer occurrence need 

 no special mention. 



To the second class, or to the non-nitrogenized substances, 

 belong : 



1. All oily and fatty matters. 



2. Starch or amylum, which constitutes the principal part 



of wheaten flour, oat and barley meal, rice, Indian 

 corn, and the dry matter of potatoes. 



3. Sugar, which abounds in mangolds, carrots, and turnips. 



4. Gum and mucilage, constituents of every kind of food. 



5. Pectin, the jelly-like substance, which is found in carrots, 



mangolds, turnips, and many other bulbous roots. 



6. Cellular and woody fibre, substances which constitute 



chiefly the bulk of straw and hay, and occur abundantly 

 in every other vegetable produce. 



These, with a few other compounds of less general occurrence, 

 constitute the class of non-nitrogenized matters. The nitrogenized 

 compounds constitute a remarkable class of organic substances. 

 They contain all about 16 per cent, of nitrogen and small 

 quantities of sulphur or phosphorus, or both, and resemble each 

 other so closely in their general properties and composition, that 

 they can scarcely be distinguished from each other. As the type 

 of this interesting class of compounds we may regard vegetable 

 albumen, a substance analogous, if not identical, in properties and 

 composition with the white of eggs. On account of the close 

 resemblance of vegetable casein, gluten, and legumin with 

 albumen, all the compounds of this group are often called 

 albuminous matter, and as they all furnish by a simple chemical 

 process a substance called protein, they are likewise frequently 



