GENERAL CONSIDERATIONS 231 



lation of a ration, the crude protein (pro terns -f- 

 non-protein nitrogenous substances) or proteins 

 alone were reckoned, but if the food were rich in 

 amides, it is possible that the animal would not get 

 sufficient proteins if the crude protein only were 

 used in the calculation. 



In order to quickly and conveniently see the 

 relation between crude protein and the various 

 nitrogen-free substances, it has been for some time 

 the custom to employ the " nutritive ratio " which 

 gives the amount of digestible nitrogen-free materials 

 of the nature of carbohydrates which falls to i 

 part of digestible crude protein. The digestible 

 portions of the nitrogen-free extract and of the 

 crude fibre are similar in their percentage compo- 

 sition and heat value to the carbohydrates (p. 69) ; 

 the fat, however, is a more concentrated nutrient, 

 and on combustion uses 2-44 times as much oxygen 

 as do the carbohydrates. Formerly the amount of 

 oxygen consumed in the combustion of a material 

 was taken as a standard of its value in the production 

 of heat and as a nutrient, so that to calculate the 

 digestible fat as carbohydrate it was multiplied by 

 2-44, and the amount added to the nitrogen-free 

 extract substances. To calculate, for example, the 

 nutritive ratio of oats, which contain 8-0 % crude 

 protein, 4-0 % fat, 44-8 % nitrogen-free extract, and 

 2-6 % crude fibre, all of which are in a digestible 

 form, the sum of the carbohydrates would be 



