GENERAL CONCLUSIONS 167 



made to affix a money value to each of the constituents 

 of food, and, having done this, to calculate the money 

 value of any food on the basis of its composition. 

 Calculations of this kind can at any time be made on 

 the basis of the market prices ; but values thus arrived 

 at are naturally variable, and by no means necessarily 

 represent the value of the food to the animal, or its 

 value as a source of manure. The relative nutritive 

 value of the various constituents of food can be esti- 

 mated on scientific grounds only on the basis of their 

 respective heat-producing powers (p. 157). From this 

 point of view, fat has more than twice the value of 

 any other food constituent ; digestible albuminoids and 

 carbohydrates have a similar value, while digestible 

 fibre is nearly equal to starch when the food is used 

 for mere maintenance, and is to be reckoned as value- 

 less when the food has to produce external work or 

 increase. If, however, the value of the food constitu- 

 ents is to include, as it must in practice, their manure 

 value, the nitrogenous substances and the ash con- 

 stituents will then become of greatest worth. The 

 manure value is at present scarcely taken into account 

 in determining the market price of foods. 



The practical effect of any food must depend, in 

 great measure, on the conditions under which it is 

 employed. Thus the value of a bulky food, as hay or 

 straw, is far greater when given to a ruminant animal 

 than when consumed by a horse or pig. Concentrated, 

 easily digestible foods, as corn and oilcake, have clearly 

 a value above their composition when added to a poor 

 and bulky food, as straw chaff, or to a watery food like 

 turnips, because they are the means of raising the 

 quality of the diet to a point at which the animal will 



