186 BOARD OF AGRICULTURE. 



speak of these — the nitrog-enous compounds — as the flesh-forming 

 substances. 



The non-nitrogenous constituents of our stock foods are starch, 

 sugar, gum, pectin, oil, and cellulose, or woody fibre in different 

 conditions of digestibility or iudui-ation. The non-nitrogenous 

 compounds are spoken of as the respiratory or heat-producing, 

 and fat-forming substances. 



Now, writers on agricultural chemistry and physiology have 

 generally assumed that it is chiefly the proportion of the nitrogen- 

 ous or so-called flesh-forming substances contained in them, which 

 determines the comparative value, for feeding purposes, of difl^er- 

 ent foods. 



The colored diagram before you will enable you to judge 

 whether or not this supposition is justified bj^ the practical ex- 

 perience of feeding. This diagram has been constructed by the 

 animals themselves. They know nothing about nitrogenous or 

 non-nitrogenous constituents, digestible or indigestible cellulose, 

 and so on ; but they are gifted with an unerring instinct, which 

 enables them not only to distinguish between substances which 

 are and ax-e not food, but also to select from a variety of food stuff's 

 those which are most suitable for the requirements of the system, 

 and so to indicate to us the proper amounts and proportions of the 

 different constituents. 



In the experiments to which the diagram refers, as well as in 

 many others, the plan has been to select foods containing very 

 different proportions of nitrogenous and non-nitrogenous com- 

 pounds ; in fact, some containing two or three times as much 

 nitrogen as others. We have then given to one set of animals a 

 small fixed amount daily, of food containing a low percentage of 

 nitrogen, and allowed them to take as much as they chose of 

 food, different in composition in this respect. To another set we 

 have given a limited amount of food, rich in nitrogenous com- 

 pounds, and allowed the animals to take, ad libitum, of a different 

 description of food, and so on. In this way they have been 

 enabled to fix for themselves the limit of their consumption of 

 nitrogenous and non-nitrogenous constituents, respectively, ac- 

 cording to their wants. 



The diagram shows the results of such experiments with pigs ; 

 and the foods employed were Indian corn meal, barley meal, bean 

 meal, lentil meal, bran, and dried cod-fish, used alone, or in com- 

 bination, as the case might be. Black being taken to represent 



