THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 163 
fat of the food as the sole source of the body fat. The contrary 
view was first propounded by Liebig * in 1843. After drawing the 
distinction between “plastic materials” (proteids), which serve to 
build up the tissue, and “respiratory materials” (non-nitrogenous 
substances), which serve as sources of heat, he asserts that any 
excess of the latter over the immediate needs of the organism is con- 
verted into fat. This proposition, which was based upon observa- 
tion and general knowledge rather than upon specific experiments, 
led to an active controversy with the adherents of the older view 
and to much direct experimental work. 
Liebig, while not denying that the food fat was a source of body 
‘ fat, maintained that the amount contributed by it was insignificant 
and regarded the carbohydrates as the chief source of animal fat. 
The controversy turned upon the question of the possibility of 
accounting for the body fat by the food fat, both parties tacitly 
agreeing that any excess was to be credited to the carbohydrates. 
The principal champions of the older view were Boussingault, Dumas, 
and Payen.t Boussingault, in particular, brought forward the 
results of experiments on milch cows, according to which the fat 
of the food fully sufficed to account for that in the milk. They 
all, however, ultimately came to acknowledge the substantial accu- 
racy of Liebig’s view. Thus Dumas & Milne-Edwards ¢ confirmed 
the results of Huber & Gundlach,§ cited by Liebig, according to 
which bees can produce wax from honey or sugar. Boussingault | 
published the results of new experiments on milch cows as sus- 
taining his previous view of the question, but later {/ convinced 
himself by careful and laborious experiments on the fattening of 
swine and geese of its untenability and of the correctness of Liebig’s 
position. Thus in one of his experiments nine pigs gained 103.2 kgs. 
of fat in ninety-eight days, while the food contained but 67.6 kgs., 
of which about 8 kgs. was excreted undigested in the feces. 
Persoz ** likewise, in experiments with geese, obtained similar 
* Ann. Chem. Pharm., 45, 112; 48, 126; 54, 376. 
+ Annal. de Chim. et de Physique., 3d ser. 8, 63. 
+ Ibid., 14, 400. 
§ Naturgeschichte der Bienen, Kassel, 1842. 
| Annal. de Chim. et de Physique., 3d ser., 12, 153 
q Loc. cit., 14, 419. 
** Annal. de Chim. et de Physique., 14, 408. 
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