NITEOGENIZED ALIMENTARY PKCSTCIPLES. 45 



united with innutritions substances from which they are sep- 

 arated in digestion. This necessitates a complicated digestive 

 apparatus. In some of the inferior animals, the quantity of 

 nutritious material forms so small a part of the food, that the 

 digestive apparatus is even more complicated than in the 

 human subject. This is especially marked in the herbivora, 

 the flesh of which forms an important part of the diet of 

 man. In addition to what are distinctly recognized as ali- 

 mentary principles, food contains many substances having an 

 important influence on nutrition, which have never been iso- 

 lated and analyzed, but which render it agreeable and give to 

 the diet a variety which the system imperatively demands. 

 Many of these principles are developed in the process of 

 cooking. They will be considered, as far as practicable, in 

 connection with the different articles of diet. 



The alimentary principles belong to the inorganic, vege- 

 table, and animal kingdoms, and are generally divided into 

 the following classes : * 



1. Organic nitrogenized principles (albumen, fibrin, ca- 

 seine 3 musculine, etc.), belonging to the animal kingdom ; 

 and vegetable nitrogenized principles, such as gluten and 

 legumine. 



2. Organic non-nitrogenized principles (sugars, fats, and 

 starch). 



3. Inorganic principles. 



Nit/rogenized Alimentary Principles. 



In the nutrition of certain classes of animals, these prin- 

 ciples are derived exclusively from the animal kingdom, and in 

 others, exclusively from the vegetable kingdom ; but in man, 

 who is omnivorous, both animals and vegetables contribute 

 nitrogenized material. In both animal and vegetable food, 

 these principles are always found combined with inorganic 



1 Inorganic and animal substances have already been considered in treating 

 of proximate principles (see vol. i., Introduction). 



