48 THE FEEDING OF ANIMALS 



(2) These compounds are structurally essential to the 

 growth of animal tissues and to the formation of milk. 

 The significance of this fact is intensified by their paucity 

 in many of the feeding-stuffs that are ordinarily pro- 

 duced on the farm. 



PEOTEIN 



For the sake of brevity and convenience, the nitro- 

 gen compounds of cattle foods, both vegetable and 

 animal, have been designated as a class by the single 

 term protein. When, therefore, it is stated that a feeding- 

 stuff contains a certain percentage of protein, reference 

 is made to the total mass of nitrogen compoimds present, 

 which may be many in number and of greatly differing 

 properties. 



60. How protein is determined. — ^The proportion of 

 protein (total nitrogen compounds) in a feeding-stuff as 

 given in tables of feeding-stuff analyses is ascertained by 

 determining the percentage of total nitrogen and then 

 multiplying this by the factor 6.25. This method is based 

 on the assumption that the average percentage of nitro- 

 gen in protein compounds is 16, which is not true to so 

 close a degree of approxunation as was formerly believed 

 to be the case. It may happen in some instances that a 

 determination made in this way is suflJciently accurate, 

 while in other cases the margin of error is large. Recent 

 investigations with perfected methods show percentages 

 of nitrogen in the numerous single protem substances 

 found, in the grains ranging from 15.25 to 18.78. These 

 are largest in certain oil seeds and lupines and smallest 

 in some of the winter grains. Ritthausen, a prominent 

 German authority, conceded that the factor 6.25 should 

 be discarded, and suggests the use of 5.7 for the larger 



