THE SELECTION OF FOODS 59 



appetite gets cloyed and when such indications appear, they 

 may be dispelled for a time at least by substituting another 

 food factor for one of those fed, or by adding it to the 

 ration without increasing the amount fed. Shepherds and 

 herdsmen who grow and fit animals for exhibition resort 

 to such methods from time to time to promote increase. 



The reasons why a change in foods thus promotes 

 increase are not all understood. It would seem correct to 

 say that they include the following : ( i ) The change may 

 meet the needs of the system more perfectly by supplying 

 nutrients that may be lacking in some degree; (2) the 

 change may lead to some chemical action that is beneficial 

 to digestion, and (3) the influence on appetite frequently 

 leads to increased consumption of food. But it should be 

 remembered that all changes are not beneficial. 



Value in foods. That the value of foods is influenced 

 by the nutrients which they contain is so evident that it 

 needs no demonstration. But to take those nutrients as 

 the true measure of their value would be a great mistake 

 as has already been shown. It is a mistake, however, of 

 too frequent occurrence. 



That the condition of the nutrients exercises a potent 

 influence on the value of foods is equally clear. Food 

 that is not digestible cannot nourish the system, although 

 in some instances it has a mission in furnishing bulk. The 

 percentage of the nutrients that go to sustain life and main- 

 tain production, is that proportion of the same which is 

 digestible. This varies greatly in plants of different varie- 

 ties and in the same plants at different stages of growth. 

 Only 21 per cent for instance of the protein in rye straw 

 is digestible, whereas 62 per cent of the protein in clover 

 hay is digestible. Relative digestibility, therefore, in the 

 value of foods is worthy of the most careful consideration 

 on the part of feeders. 



Suitability for the purpose for which foods are fed 

 cannot be given too much consideration. Some foods may 

 be used with the greatest profit in feeding certain classes of 



