iv PnEFACE. 



In the writer's view, the highest iisefuhiess of a work hko tho 

 X^resGut does not consist simply in giving receipts which shall 

 enable the f amier to feed his stock more economically, or to pro- 

 duce more milk or more or better beef, but in so elucidating 

 our knowledge of the unchanging natural laws, che;tnical and 

 physiological, of the nutrition of animals, that the attentive stu- 

 dent shall be able to adapt his i)ractice to the varj^ing conditions 

 in which he may be placed, and, more important still, shall be 

 able to appropriate intelligently the results of new investiga- 

 tions and follow or take part in the advances of the science. 



Guided by this idea, the author has not been content simj^ly 

 to state results, but has endeavored, so far as was |)ossiblc in 

 an elementary work, to indicate the processes by which these 

 results have been reached and the degree of cert-ainty which 

 attaches to them, as well as to point out the directions in which 

 om^ knowledoe is still deficient. Only in this way can a cor- 

 rect idea of the present state of the science be obtained or the 

 learner be prepared to appreciate and utilize further j)rog3*ess. 



In this the chiefly practical imx}ortance of the subject has 

 not been forgotten. 



The ultimate object of this branch of api^liod science is, of 

 course, to enable us to feed better and more economically ; but 

 the only sure and lasting foundation for a rational practice is a 

 knowledge of the natural laws on which it is based, and with 

 which it must be in accordance in order to be successful. 



This method of treating the subject naturally makes demands 

 for study and thought on the part of the reader ; the results 

 of twenty years of arduous scientific work by scores of investi- 

 gators are not to be grasped and appropriated without labor. 

 At the same time the author has endeavored to reduce this 



