RELATIVE VALUES OF FEEDING STUFFS 597 



terial sufficient to produce a quantity of milk or of meat having 

 an energy value of 85 Therms. Still further, the investigations 

 by which these facts are established also show that out of the 

 approximately 187 Therms gross energy of 100 pounds of maize 

 meal, about 50 escape unused in the various excreta, while about 

 52 are expended in the various processes connected with the 

 consumption and assimilation of the feed. In other words, they 

 show the nature of the losses suffered as well as the final amount 

 of product to be expected. Such data as these have an inde- 

 pendent value and are of an entirely different nature from those 

 expressed in the feed units. 



2. RELATIVE VALUES BASED ON COMPOSITION AND 

 DIGESTIBILITY 



705. Chemical composition. Even before the rise of the 

 system of hay values, attempts were made by Davy, Einhof, 

 Sprengel and others to compare feeding stuffs on the basis of 

 chemical analyses, and indeed the earlier hay values were 

 based in part on such comparisons (700). The methods for 

 the chemical analysis of feeding stuffs were gradually improved, 

 although they still remain quite imperfect, but along with this 

 improvement came a clearer recognition of the fact that the 

 problem of relative values is at bottom a physiological and not 

 a chemical question. 



706. Physiological functions of nutrients. In particular 

 the teachings of Liebig and the investigations of Bischoff and 

 Voit l on the nutrition of carnivora served to establish those 

 basal facts regarding the functions of proteins, carbohydrates, 

 fats and ash in nutrition which have been confirmed and ex- 

 tended by later inve*stigations and have been outlined in Chap- 

 ter V. Haubner appears to have been the earliest to suggest the 

 application of these principles to comparisons of feeding stuffs 

 and the feeding of farm animals, while to Grouven 2 belongs the 

 credit of having first formulated the requirements of animals 

 and the values of feeding stuffs in terms of the different classes 

 of nutrients. His tables, however, were based on the total 

 nutrients found by chemical analysis and were comparatively 



1 Gesetze der Ernahrung des Fleischfressers, 1860. 



2 Vortrage uber Agriculturchemie, 1858. 



