114 THE CHEMISTRY OF THE FARM. 



4. General Conclusions. Attempts have often been 

 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 mar- 

 ket 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 estimated on scientific grounds only on the 

 basis of their respective heat-producing powers (p. 109) ; 

 from this point of view fat has more than twice the value 

 of any other food constituent. If, however, the value of 

 food constituents is to include (as it must in practice) 

 their manure value, the nitrogenous substance will then 

 become of greatest worth. The manure value is at 

 present scarcely taken into account in determining the 

 market price of food. 



It is difficult, however, to affix a definite feeding value 

 to any food, as its practical effect must depend in great 

 measure on the conditions under which it is employed ; 

 more especially on the kind of animal consuming it, and 

 the general character of the diet of which it forms a part. 

 Thus the value of a bulky food, as hay or straw, is far 

 greater when given to a ruminant animal than when con- 

 sumed by ahorse or pig. Concentrated, easily digestible 

 foods, as corn and oil-cake, 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 thrive. On the other hand, 

 roots and green fodder, even when watery and poor in 



