THE COMPUTATION OF RATIONS 691 



In one respect Kellner's standards differ radically from pre- 

 ceding ones and constitute a notable advance. While the earlier 

 standards, like the earlier tables of feeding stuffs, assume di- 

 gestible protein, carbohydrates and fats from different sources 

 to be of substantially equal nutritive value, Kellner's figures 

 take account of those differences in the values of nutrients as 

 sources of energy which have been revealed by recent inves- 

 tigations and express the needs of animals in this respect in 

 what are, in fact, although not in form, net energy values. In 

 addition, his standards regard only the true protein as of 

 value and they reduce somewhat the very high requirements of 

 fattening animals for protein as postulated by early authors. 

 In other respects, however, they are on substantially the plan 

 of the Wolff -Lehmann standards, i.e., they are in form pre- 

 scriptions or recipes for rations for different purposes. 



2. FEED REQUIREMENTS 



794. Limitations of feeding standards. From the outset it 

 was necessary to guard against misconceptions arising from the 

 very definite form in which the feeding standards were pre- 

 sented. Their authors insisted from the first that they were in- 

 tended as general guides and not as fixed rules to be rigidly ad- 

 hered to. But the human mind craves a recipe and there has 

 been a persistent tendency to substitute for the study of the 

 principles of nutrition a series of exercises in applied arithmetic. 

 Others again, perhaps misled by the name, have interpreted the 

 feeding standards as representing a physiological demand of 

 the animal ; a sort of moral ideal in feeding, to be aimed 

 at, but concerning which concessions have to be made to human 

 fallibility and the pressure of circumstances. 



The difficulty inherent, more or less, in all forms of feeding 

 standards, but especially in the earlier ones, is that they fail 

 to take sufficient account of the fact that the feeding of farm 

 animals is an economic problem. A manufacturer would not 

 buy some average amount of raw material which might be re- 

 garded as the norm for his business, irrespective of the capacity 

 of his own factory or of the market for the finished product. 

 When high prices prevailed he might find it profitable to han- 

 dle a maximum amount of raw material and so to reduce the 



