INTRODUCTION. 



THE principal materials which enter into the com- 

 position of the animal body, as well as of the food neces- 

 sary for its support, may be divided into several general 



classes: 



fl. Water. 

 I. Inorganic n , r . , , . 



j 2. Mineral substances. 



^ 1. Non-nitrogenous 1 (a) Carbohydrates. 

 II Organic J compounds, such as j (5) Fats. 



" I 2. Nitrogenous compounds, such as the 

 Proteins. 



There are a number of nitrogenous compounds in the 

 animal body which cannot be classed under the proteins, 

 and others which contain no nitrogen, but which do not 

 belong to the carbohydrates or fats; nevertheless, these 

 three classes include, by far, the largest part of the organic 

 constituents. 



THE CARBOHYDRATES. 



The carbohydrates are composed of three elements: 

 carbon, hydrogen, and oxygen. The latter two are always 

 present in proportion to form water, and in this the carbo- 

 hydrates differ from the fats, which contain less oxygen. 

 The name of the group is derived from their composition, 



