244 3rAKlIAL OF OATTLE-FKEDING. 



belonging to the other four classes. It is evident that, be- 

 sides real nutrients, each of these groups of substances 

 may include many things which are wholly indigestible, 

 and hence that, although pure protein, for example, may 

 be wholly digestible, the "crude protein" of hay or straw 

 may be only partially digestible, as is actually the case. 



Furthermore, a substance which of itself is entirely di- 

 gestible may be so enclosed in indigestible matters as 

 largely or entirely to escape the action of the digestive 

 fluids. 



For example, seeds which are swallowed whole gener- 

 ally escape digestion, in spite of the fact that they consist 

 largely of digestible matters, because their hard outer coat- 

 ings slnit up the latter in an impervious shell. Similarly, 

 if the walls of a single cell are so hard and woody as to be 

 unacted on by the juices of the alimentary canal, the con- 

 tents of the cell may pass through the animal without 

 being digested. 



Finally, the relative quantities of the several nutrients 

 in the fodder of an animal have a mutual iniluence on the 

 amount of each digested. Thus, if a fodder be made over- 

 rich in starch, tlie digestibility of the albuminoids is de- 

 creased, and, at the same time, a portion of the starch 

 escapes digestion. 



All these considerations render it obvious that a simple 

 analysis is not sufficient to determine the value of a f eed- 

 ing-stuif, but that the digestibility of its constituents must 

 be teken into account, either by direct experiment or by 

 reference to the results of previous experiments. 



In this chapter we shall consider such general principles 

 as experiment has established regarding the digestibility, 

 first, of coarse fodder, and second, of the concentrated 

 bye-fodders, under the influence of various conditions, and 



