THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 183 
arch aiake Total Fat Gain per 
Equivalent | Equivalent | Kilogram 
of Nutrients of Gain, Nutrients, 
ane Grms. Grms. 
Ox H: 
Extracted straw, period 5-4......... 2425 613 252.8 
Starch, 8-4... 1695 395 233.0 
xe J: 
Extracted straw, period 5-4......... 2334 509 218.1 
Starch, e ee eer aera 1370 284 207.3 
by the addition to the basal ration of digestible matter five sixths 
of which was derived from crude fiber, was not inferior to that 
‘produced by the addition of an equal amount of pure starch. 
It would seem that these results may fairly be taken as showing 
that the products of the digestion of cellulose by ruminants are 
substantially of equal value with those of the digestion of starch. 
This, however, by no means warrants the conclusion that starch and 
cellulose are of equal value in ordinary feeding-stuffs. The mate- 
rial used in these experiments had been so altered mechanically 
and freed from incrusting materials by the treatment to which it 
had been subjected that 88.3 per cent. of its organic matter and 
95.8 per cent. of its crude fiber was digested. The same animals 
digested but 52.5 per cent. of the crude fiber of wheat straw, and 
the digestible organic matter of the latter proved far less efficient 
than that of either starch or extracted straw. A full discussion of 
these facts may be more profitably undertaken in connection with a 
consideration of the energy relations of feeding-stuffs in Part I; 
for the present it may suffice to point out that the difference just 
noted appears to depend on physical rather than chemical causes. 
Pentose Carbohydrates.—We have already (p. 156) seen reason 
to believe that the pentose carbohydrates may serve as a source of 
energy to the organism and protect other materials from oxidation. 
This, of course, is equivalent to an indirect production of fat. In 
the same connection, however, the experiments of Kellner, just 
mentioned, were referred to as indicating a direct participation by 
these bodies in fat production. About one third of the digested 
matter of the extracted rye straw was found to consist of bodies 
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