100 MANUAL OF PHYSIOLOGY. 



live stuffs are exclusively destined to replace corresponding sub- 

 stances in the body. On the contrary, we have good reason to 

 think that within the body the conversion of one group into an- 

 other is very common. 



In Chapter III, the tissues of the animal body were shown to 

 consist of chemical compounds, which have been classified into 

 certain groups. And it has also been stated that the tissues are 

 constantly undergoing chemical changes inseparable from their 

 life, and that for these changes a supply of nutritive material is 

 necessary. 



The nutriment required for an animal is, then, made up of 

 substances which may be divided into the same chemical groups 

 as the tissues of the body : viz., proteids, fats, carbohydrates, 

 salts and water. So that each of the various substances which 

 we make use of as food, contains in varying proportions several 

 of the different kinds of nutrient material, either naturally or 

 artificially mixed so as to form a complex mass, the important 

 item water being the only one which is commonly used by itself. 

 These substances may be considered to be the chemical bases of 

 the food, as they are also the chemical bases of the animal body. 



The following classification shows the relationships between the 

 chief items of nutritious matters, from a chemical point of view, 

 and their distribution in the various foods we commonly eat. 

 I. ORGANIC. 



1. Nitrogenous 



A. Albuminous abundant in eggs, milk, meat, 



peas, wheaten flour, etc. 



B. Albuminoid in soups, jellies, etc. 



2. Non-Nitrogenous 



A. Carbohydrates (sugar, starch) abundant in 



all kinds of vegetable food, and in milk, and 

 present in small quantity in meat, fish, etc. 



B. Fats in milk, butter, cheese, fat tissues of 



meat, many vegetables, oils, etc. 

 II. INORGANIC. 



1. Salts mixed with all kinds of food. 



2. Water mixed with the foregoing or alone. 



