THE RELA TIONS OF METABOLISM TO FOOD-SUPPLY. 179 
periments in which the conditions were favorable for a production 
of fat from carbohydrates, some actually do show that result, al- 
though they were classed by Voit as “exceptional cases,” while its 
failure to appear in others is explained, according to Pfliiger, by the 
increased metabolism due to maltreatment of the animal and the 
overloading of its digestive organs with starch. 
Whether we admit all of Pfliiger’s criticism or not, it is now uni- 
versally conceded that the carbohydrates are an important source 
of fat. If we are to go further and deny with Pfliiger the production 
of fat from proteids, we are brought back, by a curious reversal of 
views, substantially to Liebig’s classification of the nutrients into 
“plastic” and “respiratory,” but, as already pointed out, it ap- 
pears altogether probable that the proteids also contribute to fat 
production. However this may be, it is clear that in the case 
of herbivorous animals, which ordinarily consume relatively little 
proteids and fat and large amounts of carbohydrates, the latter are 
the most important factors in fattening, and the results of Lawes 
& Gilbert (p. 167), according to which the gain of fattening ani- 
mals is largely determined by the supply of non-nitrogenous matters 
in the food, are seen to be in full accord with the most careful physi- 
ological investigation. 
Evidence from Respiratory Quotient—The formation of fat from 
carbohydrates is a process of reduction. If we suppose all the car- 
bon of 100 parts of dextrose, together with the necessary hydrogen 
and oxygen, to be united to form fat of the average composition 
stated on p. 61, we have the following: 
Dextrose. | auivalent.! Residue, | Pquivalent,) Excess of 
Carbon...........6-- 40.00 40.000 |eivcasscclesevevcssleccevayses 
Hydrogen........... 6.67 6.28 0.39 02.39) less cee ees 
OXYEED a2 esses ne eene (53.33 6.01 47.32 3.12 | 44.20 
100.00 52.29 47.71 3.51 44.20 
The excess of oxygen we may further suppose to unite with the 
carbon of 41.44 additional parts of dextrose, producing 60.78 parts 
of carbon dioxide and 24.86 parts of water. The process would be 
an intra-molecular combustion analogous to a fermentation, pro- 
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