122 The Feeding of Animals 



tion. The low digestibility of wheat straw, as compared 

 with that of the wheat kernel, is due to the absence in 

 one of compounds that are abundant in the other. We, 

 therefore, must deal fundamentally with the suscepti- 

 bility of the various single constituents of plants to the 

 dissolving action of the several digestive ferments. 



In this connection, we need to pay little attention to 

 the mineral compounds. They do not undergo fermen- 

 tative changes in the way that the carbon compounds 

 do, but pass into simple solution either in the water 

 accompanying the food, or in the juices with which they 

 come in contact. 



As has been noted, protein is a mixture of nitrog- 

 enous compounds, largely albuminoids. The gluten of 

 wheat contains at least five of these bodies, and other 

 seeds as many. What is the relative susceptibility of 

 these single proteids to ferment action either as to ra- 

 pidity or completeness of change does not appear to be 

 known. Some albuminoids are practically all digested 

 by artificial methods, and probably are in natural di- 

 gestion. It is a fact, however, that protein is much 

 more completely dissolved from some feeding stuffs than 

 from others. That of milk is all digestible, that of some 

 grains very largely so, while with the fodders quite a 

 large proportion escapes solution. Whether this is due 

 to a differing degree of solubility on the part of the 

 characteristic protein compounds of these feeding stuffs 

 is not quite determined. The fact that highly fibrous 

 materials show the lowest proportion of digestible pro- 

 tein suggests as an explanation that the nitrogen com- 

 pounds of the coarse fodders are so protected by the 



