iv. Preface to the Fourth Bevision. 



been made for the present revision are very con- 

 siderable, the largest changes being made in the 

 sections relating to the nutrition of animals. These 

 alterations have been rendered necessary by the pub- 

 lication of the epoch-making investigations of Zuntz 

 and Hagemann on the nutrition of the horse,^ and 

 of the equally important researches of Kellneb, 

 KoHLEE, and their associates, on the nutrition of the 

 ox.' By these laborious researches many important 

 problems have been solved, and a foundation laid on 

 which a really accurate science of feeding may be 

 constructed. 



In the new work of these German investigators, 

 both the value of the food, and of the work which it 

 undergoes, or accomplishes, is reckoned in units of 

 heat. The fundamental facts established by their 

 investigations have been brought together in a sepa- 

 rate chapter (VII.). The discussions in this chapter, 

 while introductory to much that follows, unavoidably 

 assume a knowledge of some facts afterwards men- 

 tioned ; students using the book will therefore do well 

 to refer to this chapter several times in the course of 

 their subsequent reading. 



The chapter on Dairy Chemistry has been consider- 

 ably enlarged ; and here the writer has been indebted 

 to the work of Mr. H. Dboop, Richmond, for much 

 of the new matter which has been introduced. 



As this book is intended for the use of students, 



• Untersuchungen iiber den Stoffwechsel des Pferdes bei Ruhe und 

 Arbeit, von N. Zuntz und O. Hagemann, Berlin, 1898. 



^ Untersuchungen iiber den StofE-und-Energie-Umsatz, des erwach, 

 senen Rindcs bei Erhaltungg-und-Produktionsfutter, von 0. Kellner, 

 Berlin, 1900. 



