‘METABOLISM. 55 
ticularly of the carbohydrates of the food, as is shown by the large 
amounts of gaseous hydrocarbons produced by these animals. In 
carnivora, on the contrary, digestion is relatively rapid and the 
dog, as a representative of this class, excretes, according to Voit & 
Pettenkofer,* but traces of hydrocarbons, and according to Tap- 
peiner,} none. 
Zuntz { has therefore suggested that soluble amides introduced 
into the digestive canal of herbivora may be used as nitrogenous 
food by the micro-organisms there present in preference to the less 
soluble proteids, so that the latter are to a certain extent protected, 
and that it is even possible that the amides are synthesized to 
proteids by the organisms. Hagemann § has added the suggestion 
that the proteids possibly thus formed may be digested in another 
part of the alimentary canal and thus actually increase the pro- 
teid supply of the body. 
If this explanation is, correct, we should expect the effect of 
asparagin to be more marked when the proportion of proteids in 
the food is small, and precisely this appears to be the case. In 
Weiske’s first experiments, which gave the most decided results, 
the nutritive ratio of the ration without asparagin was 1:19-20, 
while a later experiment with a nutritive ratio of 1:9.4 showed no 
effect of the asparagin upon the gain of protein. Chomsky’s results, 
too, were obtained with rations poor in protein and rich in carbo- 
hydrates. 
Later experiments on lambs by Kellner || have fully confirmed 
this anticipation. In his first experiment two yearling lambs were 
fed with a mixture of hay, starch, and cane-sugar, having a nutri- 
tive ratio of 1:28, until nitrogen equilibrium was reached, when ~ 
fifty grams of the starch was replaced by asparagin. The result 
was a gain of protein by both animals as compared with a loss in 
the first period. In the third experiment asparagin was substi- 
tuted for starch in a ration having a nutritive ratio of 1:7.9, and 
caused with one animal a slight gain and with the other a slight 
loss of protein. In the fourth experiment it was added to a ration 
* Zeit. f. Biol., 7, 433; 9, 2 and 438. 
t Ibid., 19, 318. 
tArch. ges. Physiol., 49, 483. 
§ Landw. Jahrb., 20, 264. 
|| Zeit. f. Biol., 39, 313. 
