XVI INTRODUCTION 



the transformation may be effected with the least possible waste, 

 and, on the other hand, the ability so to apply these laws as to 

 secure the greatest economic return, since it must never be 

 forgotten that the criterion of success in agriculture is not a 

 maximum production but a maximum profit. It is with the 

 former portion of this complex problem that the present work 

 attempts primarily to deal. 



Without entering into the controversy between the vitalist 

 and "the mechanist, the nutrition of the animal, whatever its 

 guiding principle, may be regarded as a physico-chemical pro- 

 cess, including the entire complex of reactions by which the 

 crude materials of the feed are converted into substances suited 

 to maintain the activities of the body cells or capable of being 

 built up into living structures. In other words, the study of 

 nutrition is a study of the chemistry and physics of the changes 

 through which the crude products of the soil yield animal tissues 

 or secretions on the one hand and excretory products on the 

 other. 



The earlier investigators dealt with the food as a supply of 

 matter, dividing it into inorganic and organic constituents and 

 distinguishing among the latter between the nitrogenous and 

 non-nitrogenous substances. In other words, they studied the 

 problems of nutrition substantially as problems of biological 

 chemistry. Rubner's fundamental investigations went far to 

 shift the emphasis to the physical side of the problem. It has 

 come to be clearly recognized that the animal body is essen- 

 tially a transformer of energy a mechanism for the conversion 

 of the chemical energy of its feed into mption energy while 

 more or less incidentally a reserve of energy-containing material 

 may be stored up which can be utilized for human food. It is 

 this capacity of the animal body to store up in itself or in its 

 secretions a part of the matter and energy of the feed it con- 

 sumes which gives the animal its economic significance as a 

 conserver of the food supply. Its value in this respect depends 

 upon the proportion of its feed which it is able thus to set 

 aside i.e. upon the balance between the income and outgo 

 of matter and of energy and it is from this point of view that 

 the present volume undertakes to present the nutrition of farm 

 animals. From this standpoint, the subject naturally falls into 

 four principal divisions. 



