THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 125 
cherry gum, containing 41.98 per cent. of pentose carbohydrates, 
the urinary nitrogen of a horse decreased by over 6 per cent. They 
leave it uncertain, however, whether the effect was due to the 
pentosans or to other ingredients of the gum. 
Among the early experiments of Grouven * are also four in which 
gum arabic, added to an exclusive straw ration, materially reduced 
the proteid metabolism, but the methods of these early experiments 
were naturally somewhat defective. On the other hand, Cremer’s 
experiments ¢ with rhammose on rabbits showed no marked effect 
of this substance upon the proteid metabolism. 
Total Non-nitrogenous Matter of Feeding-stuffs.—The digestible 
non-nitrogenous matters of feeding-stuffs, aside from a small pro- 
portion of fat, are commonly although loosely grouped together as 
carbohydrates. They include both hexose and pentose carbohy- 
drates, such organic acids as may be present or as are formed during 
digestion, and a variety of other less well-known substances. 
As has already appeared in discussing the effect of crude fiber, the 
mixture of material included in the digestible crude fiber and nitro- 
gen-free extract shows the same tendency as starch and sugar to 
diminish the proteid metabolism. In other words, while the com- 
mon designation of digestible carbohydrates may be of questionable 
accuracy from a chemical point of view, nevertheless the some- 
what heterogeneous mixture to which it is applied behaves, in this 
respect at least, qualitatively like the pure hexose carbohydrates. 
Numerous instances of this are cited by v. Wolff { in his discus- 
sion of the data prior to 1876. Of more recent results, attention 
may be specially called to those of Kellner, some of which have 
been cited above. The results upon coarse fodders are those which 
are of particular interest, since it is these whose ingredients are 
least known chemically. They are presented on the following 
page in the same form as those upon extracted straw above. 
Although the addition of hay or straw to the basal ration in- 
creased the supply of digestible nitrogenous matter, the proteid 
metabolism was not proportionately increased, but in every instance 
* Wolff, Ernihrung Landw. Nutzthiere, p. 289. 
} Zeit. f. Biol., 42, 451. 
{ Ernihrung Landw. Nutzthiere, pp. 288-309. 
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