THE EXCREMENTS OF MAN AND ANIMALS. 
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in the castings of hibernating animals. I am not, however, aware whether it has 
been as yet extracted from those of the Crocodile. 
The occurrence of cholesterine in the excrements of the Crocodile, and not in 
those of the Boa or any other animal which I have examined, is a phenomenon 
worthy of notice. It may be concluded from it, that a portion only of the bile 
secreted by the Crocodile is modified or absorbed during digestion, and the rest 
eliminated with the casting. 
Boa . — I treated the castings of the Boa in the same way as those of the Croco- 
dile, but without finding cholesterine. It has already been observed that the above 
method was applied to the examination of bile, and that cholesterine was obtained ; 
so that had any cholesterine been present in these castings, it could not have escaped 
observation. 
Leopard . — The castings of the Leopard were also examined; the lime precipitate in 
the alcoholic extract having been treated with ether, and the ether allowed to evaporate 
spontaneously, yielded a mass of light colourless crystals, readily reflecting light, and 
resembling those obtained in similar circumstances from the Dog and Tiger, but not 
mixed with the red amorphous substance. 
In conclusion, the castings of the carnivorous mammalia appear to contain the 
peculiar light crystalline substance, differing in its properties from excretine, and 
obtained from the ethereal extract of the lime precipitate above described. I have 
constantly failed to detect excretine as a constituent of these castings. 
The excrements of the carnivorous mammalia also contain butyric acid, or some 
of its salts, while in no case have I been able to obtain this substance from 
human faeces, where it was thought to exist. There is probably, therefore, some 
chemical change going on in the intestines of these animals different from what 
occurs in the human alimentary canal, and the butyric acid, unless it be secreted 
from the mucous membrane of the intestines, must result from some change which 
the animal food undergoes in the intestine during the process of digestion. It is not 
impossible that some of the sugar elaborated by the liver may be converted into 
butyric acid in the circulation and eliminated through the intestines. 
The fseces of the Crocodile and Boa materially differ from each other, the former 
containing cholesterine, but no uric acid, and the latter being nearly entirely com- 
posed of urates, but containing no cholesterine. The rule applied to hibernating 
animals meets here with an exception ; further investigation is therefore necessary 
before any positive and general law can be arrived at. 
3. Of the Castings of Herbivorous Animals. 
The castings of the Horse , Sheep , Dog fed upon bread , Wild Boar , Elephant, and 
Monkey were next examined : in no case could I succeed in detecting the presence 
of excretine or of butyric acid as one of their constituents. 
