316 



ARID AGRICULTURE. 



PROTEIN 



CARBO- 

 HYDRATES 

 AND PATS 



other tissues, and in the secretions of the animal, 

 they are everywhere abundant, and outside of an 

 extra supply of common salt no attention need be 

 given them in compounding a balanced ration. 



Those organic compounds, which contain ni- 

 trogen, are classed as protein. The principal 

 forms of protein are albumen, represented by 

 the white of eggs ; gluten, the gummy substances 

 of wheat and other grains, and casein, repre- 

 sented by the curd of milk. These nitrogen com- 

 pounds are called albuminoids. There are a 

 large number of albuminoids known as amides. 

 They differ from proteids in being soluble in 

 water and are not coagulated with heat. They 

 are abundant in the green parts of plants. Good 

 examples are asparagin, abundant in asparagus, 

 and the soluble part of meat which forms the 

 principal part of beef tea. The nutritive value 

 of the amide compounds is not well known, 

 though they are probably much less valuable than 

 the proteids. 



The carbo-hydrates and fat are compounds 

 of carbon with hydrogen and oxygen. Starch 

 and sugar and crude fibre or cellulose are carbo- 

 hydrates. The fats are like the carbo-hydrates 

 in being formed of the same elements, but they 

 contain a larger proportion of carbon and their 

 heating value is about two and one-fourth times 

 as much as the sugars and starches, so they are 



