70 AGRICULTURAL EXPERIMENT STATION. 



(2) The supply of the waste caused by muscular activity. 



( 3 ) As fuel, which is consumed iu keeping up the bodily warmth. 

 What relation do the various parts of the food sustain to this 



work? The ingredients of cattle foods, as before enumerated and 

 explained, are the ash (mineral matter), protein (nitrogenous 

 substance), fats or oils, and sugar, starch, gums, &c. 



Here we have on the one hand the work to be done, and on the 

 other the means with which to do it. We must first consider 

 whether all the above kinds of material are necessary for running 

 the animal machine, or whether any one of the ingredients named 

 can perform the variety of work that is demanded. In other 

 words, have the ash, albuminoids, fat and starch peculiar parts to 

 play in the animal economj'^, or can they be used indifferently in 

 any direction where they seem to be most urgently needed? 



The investigations of physiologists and chemists have answered 

 this question, and the following may be stated as safe conclusions : 



(1) The chief office of the ash of plants is to furnish the bony 

 framework of the animal, besides which it supplies certain mineral 

 compounds that take part in the digestive processes, and that are 

 distributed in small quantities throughout the flesh. 



(2) Protein (albuminoids) is the only source of lean meat, hair, 

 horn, hoof or any other nitrogenous substance that becomes incor- 

 porated into the animal body. Fat is formed from it, in some in- 

 stances chiefly perhaps, as in the case of butter fat. It also plays 

 an indispensable, but not fully explained, part in the maintenance of 

 muscular activity, and its decomposition must contribute something 

 to the heat supply of the bod}'. In fact, experience shows that iu 

 the absence or deficienc}'^ of the other food ingredients, except the 

 Biineral compounds, albuir»inoids can, for a time at least, serve to 

 maintain all those vital processes which otherwise would wholly or 

 in part be supported by the fats and carbohydrates. 



(3) The vegetable oils and the carbohydrates are alike in being 

 fat and heat formers. Their combustion is also somehow connected 

 with the maintenance of muscular activity. 



In the matter of quantity the fats or oils are relatively' unimpor- 

 tant as compared with carbohydrates, and in the case of ordinary 

 cattle foods, the latter class of compounds makes up a very large 

 part of the nutritive substance. The carbohydrates serve to supply 

 the most of the needed fuel, and are important as a source of fat. 



