70 NUTRITION OF FARM ANIMALS 



seeds and for lupines, and 6.0 for barley, maize, buckwheat, 

 soybean, white bean, and rape and other brassicas. 



For various classes of human foods, Atwater and Bryant l have 

 proposed the following factors for the computation of protein 

 from protein nitrogen : 



Animal foods 6.25 



Wheat, rye, barley and their manufactured products . . . . 5.70 

 Maize, oats, buckwheat and rice, and their manufactured 



products 6.00 



Dried seeds of legumes 6.25 



Vegetables 5.65 



Fruits 5.80 



For feeding stuffs whose proteins have not yet been studied, 

 there seems to be no reason for changing from the present 

 usage. 



With the non-proteins the case is even more perplexing in 

 view of the greater variety of substances included under this 

 term and the wide range of their nitrogen content. The 

 writer has used tentatively 4.7, the factor for asparagin (66), 

 one of the most widely distributed substances of this class, but 

 the choice of this factor is substantially arbitrary. 



108. Crude fat. Ether extract. The methods for de- 

 termining the fat content of feeds are based upon its extrac- 

 tion by means of some solvent which dissolves as little as 

 possible of the other ingredients. A variety of solvents has 

 been used for this purpose, such as carbon disulphid, carbon 

 tetrachlorid, petroleum ether and the like, but the one most 

 commonly employed is ethyl ether, or the so-called " sulphuric " 

 ether commonly used as an anaesthetic. 



All the various solvents used, however, remove other sub- 

 stances besides neutral fats and fatty acids, including more or 

 less of the more complex lipoids. In particular the ether ex- 

 tract obtained from coarse fodders contains a variety of waxes, 

 resins, etc., as well as the chlorophyl of the leaves, and a rela- 

 tively small proportion of true fats. It is customary, there- 

 fore, to designate the extracted material as " crude fat " or, 

 since ether is the reagent ordinarily used, as " ether extract." 



1 Storrs (Conn.) Agr. Expt. Sta., Rpt., 12, 79. 



