100 NUTRITION OF FARM ANIMALS 



substances which render them innocuous. In particular, they 

 unite with sulphates to form the so-called ether-sulphates which 

 are excreted in the urine. The amount of these substances in 

 the urine furnishes a convenient index to the extent of intestinal 

 putrefaction. 



141. The non-proteins. As ordinarily determined (61, 

 106), the non-proteins constitute a group of nitrogenous sub- 

 stances soluble in water, many of which are identical with or 

 closely related to the final products of the digestion of the 

 proteins. Accordingly, they have generally been assumed to 

 be ready for resorption without further action by the digestive 

 juices and therefore to be entirely digestible. 



It has been shown, however, that, in ruminants at least, the 

 matter is by no means so simple as the mere resorption of water- 

 soluble substances. In the capacious first stomach of these 

 animals, the non-proteins play an important role as a supply 

 of nitrogenous food for the organisms which are so abundant 

 there. This has several consequences. 



In the first place, it appears that these soluble compounds 

 are more readily attacked and utilized by the organisms than 

 are the true proteins of the feed. The presence of non-proteins, 

 therefore, tends to protect the proteins from bacterial decom- 

 position. 



In the second place, an abundant supply of soluble nitrogenous 

 matter stimulates the multiplication and activity of the or- 

 ganisms and so brings about a more extensive fermentation of 

 the carbohydrates of the feed, as is evidenced by an increase 

 in the methane given off and in the proportion of the carbo- 

 hydrates apparently digested. 



Third, it seems to be fairly well made out that the nitrogen 

 which these organisms assimilate is utilized to build up their 

 protoplasm and thus, by a sort of symbiosis, becomes a source 

 of protein to their host. It has been claimed that this bacterial 

 protein is indigestible, but the evidence on which this claim 

 is based is capable of a different interpretation and there seems 

 to be good reason for believing that it may be acted on in the 

 stomach and intestines by the digestive enzyms like other pro- 

 teins and serve as a source of protein to the body. Some of 

 the evidence in favor of this view is presented in a subsequent 

 discussion of the nutritive value of the non-proteins (786-789). 



