FUNCTIONS OF THE NUTRIENTS 189 



to 67 per cent. The corn-plant pentosans were digested 

 most fully and those from the wheat plant least so. 



Swartz concluded from extensive investigation that 

 the water-soluble hemicelluloses are resistant to the 

 action of enzyms and disappear from the digestive tract 

 only in proportion as they are attacked by bacteria. 

 Pentosans and mannans which are hydrolized by bacterial 

 action were found to be almost wholly digested, while 

 galactans were largely excreted as such. In considering 

 their digestibility the groups of hemicelluloses evidently 

 must be considered separately. In any case, digestibility 

 should not be considered as a measm-e of nutritive 

 value. 



273. Relative importance of the nitrogen compounds 

 of feeding-stuffs. — ^What is known as the crude protein 

 of feeding-stuffs is the total nitrogen multiplied by the 

 factor 6.25. As has been stated, protein as so estimated 

 contains a variety of nitrogen compounds that are unlike 

 in character and exist in various cattle foods in greatly 

 unlike proportions. For example, a much larger part of 

 the crude protein of coarse fodders and roots consists of 

 amides than is the case with grains, the latter being cor- 

 respondingly richer in true proteins. If, therefore, it is 

 found that the true proteins differ from the amides in 

 function and value, we have established one point of 

 unlikeness between grain foods and roots or the coarse 

 fodders. We have convincing proof that the true pro- 

 teins are the main flesh-formers found in cattle foods. 

 Are the amides such as glutamin and asparagin also flesh- 

 formers? Eariier experiments with these compounds led 

 to the conclusion that they may exercise a protective 

 function toward the true proteins and thus reduce the 

 minimum of such proteins necessary to satisfy the needs 



