THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 181 
preceding pages, however, this is far from being the case as regards 
the materials actually resorbed from the digestive tract of our 
common domestic animals, particularly the ruminants. A demon- 
stration of the production of fat from carbohydrates, therefore, 
does not necessarily show that the chemically diverse materials 
resorbed from coarse fodders, e.g., are available for fat produc- 
tion. 
As a matter of fact, however, what a large proportion of the 
experiments just cited actually show, under a strict interpretation, 
is that fat was produced from the non-nitrogenous nutrients of the 
rations other than fat. In many of the experiments, it is true, nota- 
bly those with swine and with geese, the ration consisted of concen- . 
trated feeding-stuffs whose “nitrogen-free extract” consisted to a 
large extent of hexose carbohydrates. Similarly, in G. Kiihn’s ex- 
periments the fat production was secured by the addition of starch 
to rations slightly above the maintenance requirement. In these 
cases, therefore, at least the larger part of the fat production in 
excess of that possible from proteids and food fat must be ascribed 
to the hexose carbohydrates. In experiments like those of Henne- 
berg, Kern & Wattenberg, and of Jordan, on the other hand, a 
not inconsiderable proportion of the non-nitrogenous nutrients 
was necessarily derived from coarse fodders and was, therefore, 
largely of undetermined nature. In such cases it is obviously im- 
possible to say whether the fat production was at the expense of 
the hexose carbohydrates only or whether the other non-nitrog- 
enous ingredients participated in it. 
Other considerations, however, seem to render a participation 
of these substances in fat production, directly or indirectly, at least 
highly probable if not certain. 
Crude Fiber —The experiments of v. Knieriem (p. 161), as we 
have seen, seem to show that digested cellulose may be as efficient as 
other carbohydrates in protecting the body fat,—that is, as part 
of a maintenance ration. The numerous experiments cited on 
pp. 117-123 likewise indicate that it has an effect similar to that of 
other carbohydrates in diminishing the proteid metabolism. Kell- 
ner * has also investigated its value in a fattening ration, using for 
this purpose the material resulting from the treatment of rye straw 
* Landw. Vers. Stat., 53, 278. 
