162 PRINCIPLES OF ANIMAL NUTRITION. 
As we have seen, there has been considerable study of the effects 
of crude fiber on the proteid metabolism, but no other comparative 
experiments appear to have been made regarding the replacement 
values of cellulose and other carbohydrates i in a maintenance ration. 
The somewhat lower value which seems to be indicated for the 
organic acids by the experiments cited in the previous paragraph 
has been made the basis of conclusions as to the inferior nutritive 
value of cellulose, and Zuntz,* in some comments on Mallévre’s 
experiments, remarks that the apparent equality between cellulose 
and starch observed in experiments on ruminants is to be explained 
by the fact that in these animals the starch also undergoes 
fermentation, a fact which the researches of G. Kithn at Méckern 
have since established. In other words, he would say that in case 
of ruminants the starch has as low a value as the cellulose rather 
than that the cellulose has as high a value as the starch. 
Kellner has recently obtained results, to be discussed a little 
later, which seem to prove a participation by the digested cellulose 
in actual fat production to as great an extent as by starch, and 
which therefore seem to put the nutritive value of the form of cellu- 
lose used by him beyond dispute. 
Utilization of Excess of Non-nitrogenous Nutrients. — No 
elaborate scientific investigation is needed to teach us that food 
supplied in exceess of the immediate demands of the organism re- 
sults in a greater or less storage of material i in the body, this material 
consisting, in the mature animal, largely of fat. But while the fact 
of fat formation is obvious, the exact source of the fat has been the 
subject of as much controversy as almost any physiological question. 
As we have seen in the previous section, opinions are still far from 
being unanimous as to the production of fat from proteids, while 
until quite recently the same might have been said regarding 
the carbohydrates as a source of fat. A very complete critical re- 
view of the literature of the subject of fat formation in the animal 
body was published by Soskin f in 1894, and to this the writer is in- 
debted for a considerable number of the statements and references 
on the succeeding pages. 
As was stated on p. 29, the older physiologists looked upon the 
* Arch. ges. Physiol., 49, 447. 
} Jour. { Landw., 42, 157. 
