FOOD EEQUIREMENTS 377 



percentage of the respective digestible constituents by these 

 factors and then deducting a certain percentage of the total. 

 The deduction is supposed to represent the loss of fat- 

 forming value due to energy expended in " the work of 

 mastication and of digestion." It includes loss in fer- 

 mentation and in the non-nitrogenous substances in the 

 urine. The percentage to be deducted is indicated in 

 Kellner's tables, where each food-stuff is assigned a " value " 

 which varies roughly, inversely with the amount of crude 

 fibre in the food. The lower the value the greater is the 

 percentage to be deducted. It is taken as 100 minus the 

 value number. The method of calculation is shown by the 

 following example given for rape cake : — 



24-8% digestible proteins x 0-94 = 23-37^ starch equivalent. 



6-3% digestible fat x 2-41 = 15-27^ 



20-5% digestible nitrogen 



— free extract + 



crude fibre x 1 '00 = 20-57^ 



Total . 59'0°/o starch equivalent. 



The "value" of rape cake is 95, so 5 per cent, is 

 deducted. The final result, 56 per cent., is termed the 

 " staTch value," or "starch equivalent" of rape cake. It 

 means that 100 lbs. of rape cake is equal in value to 56 

 lbs. of starch. 



Certain modifications of the method of calculation are 

 advised in the case of food stuffs containing much crude 



fibre. 



In Kellner's standards, food requirements are stated in 

 lbs. of protein and lbs. of starch. In the tables showing the 

 composition and digestibility of the various food- stuffs, a starch 

 value is assigned to each. The object aimed at in the system 

 is to give a common basis for comparing the productive value 

 of the various feeding stuffs. 



This starch equivalent method of comparing the values of 

 food-stuff is widely used in this country. It is of doubtful 

 value. The use of a pound of starch as the unit for 



