12 PRINCIPLES OF ANIMAL NUTRITION. 
digested. In the long and complicated digestive apparatus of 
herbivora, however, there is the possibility that a variety of proc- 
esses may go on aside from a simple solution of nutrients by the 
digestive fluids. In particular, it has been shown, as will appear in 
greater detail later, that extensive fermentations, particularly of the 
carbohydrates, occur, and that relatively large amounts of these 
bodies may be destroyed in this way. 
Furthermore, with our present conventional scheme for fodder 
analysis, we have to take account of the possibility of the conversion 
of members of one group of nutrients into those of another. For 
example, it seems not improbable that a portion of the crude fiber 
of feeding-stuffs may be so modified in the digestive tract, without 
being actually dissolved, that, in the feces, it is determined as 
nitrogen-free extract, thus diminishing the apparent digestibility 
of the latter group and increasing that of the crude fiber.* 
Composition oF Diczstep Foop.—The proteids during the 
process of digestion are largely converted into proteoses and pep- 
tones, while the trypsin of the pancreatic juice, at least outside the 
body, carries the cleavage of the proteid molecule still further and 
gives rise to comparatively simple, crystalline bodies. It is not 
altogether clear to what extent this degradation of the proteids 
occurs in natural digestion, but the probability appears to be that 
it does not play a large part, and it has been generally believed that 
the proteids are resorbed chiefly as proteoses and peptones. 
The non-proteids being largely crystalline bodies and readily 
soluble, we may presume that they are resorbed without material 
change except so far as they may serve as nitrogenous food for the 
micro-organisms of the digestive tract. 
The jat of the food does not undergo any profound change in 
digestion, but appears to be resorbed largely in the form of an 
emulsion. A part of it, however, is undoubtedly saponified by 
the bile, although the extent to which this process takes place is a 
disputed point, while in some cases at least a cleavage into glycerin 
and free fatty acids appears to take place. 
The carbohydrates, particularly the easily soluble members of 
the hexose group, are in the case of man and the carnivora, and 
*Cf. Fraps, Jour. Am. Chem. Soc., 22, 543. 
