278 
DR. MARCET ON THE IMMEDIATE PRINCIPLES OF 
2nd. Castings of a Dog fed upon meat . — Fresh castings from a Dog, fed in my 
laboratory for several months upon meat alone, were next examined. They had an 
alkaline reaction and a dark brown colour. When washed with a little water 
and boiled with alcohol, they yielded an alcoholic solution, of a red colour when 
seen by reflected light and possessed of a slightly acid reaction. Put aside in a beaker 
for twenty-four hours, very little or no deposit occurred. The extract was mixed 
with lime-water, which caused the formation of a very light yellow precipitate. I 
treated it with ether, as in the previous cases, and allowed the ethereal solution to 
evaporate spontaneously. After four days, a shining crystalline deposit was observed 
floating in the liquid, which exactly resembled the substance obtained under similar 
circumstances from the castings of the Tiger. The filtrate from the lime precipitate 
having been concentrated on the water-bath, was soon observed to be full of crystals 
floating in the fluid in the form of white masses. When viewed with the microscope, 
they were found to be elongated prisms irregularly grouped in large masses. Heated 
upon a platina knife, they burnt with a flame, and left an ashy residue composed 
of lime. When a drop of sulphuric acid was added to some of the crystals dried 
on filtering-paper, and heat subsequently applied, a distinct smell of rancid butter, 
peculiar to butyric acid, was evolved, showing them to be butyrate of lime. After 
some days, the solution of the salt in alcohol, previously filtered through animal 
charcoal to remove the colouring matter, yielded by spontaneous concentration a 
number of perfectly white globular masses of crystals about the size of a large pin’s 
head, which, when dried upon filtering-paper, assumed a beautiful silky appearance. 
In conclusion, the castings of dogs fed upon meat contain butyric acid, but whether 
it be in the form of a free acid or of a salt, I have not yet satisfactorily ascertained. 
Crocodile's Excrements . — During a visit to the Zoological Gardens, I had an 
opportunity of obtaining from the crocodile’s cage a small quantity of the fresh 
castings of this animal. They had a peculiar foetid smell, and when dried could be 
easily pounded into a white powder, some of which, treated with nitric acid and 
ammonia, failed to denote the presence of uric acid. The pounded mass, after 
having been converted into a paste with a few drops of distilled water, and then 
boiled with alcohol in a glass flask, was thrown upon a calico filter. The filtrate 
having been a few hours afterwards mixed with lime, a yellow precipitate was thus 
produced ; this precipitate was subsequently filtered and boiled with ether. The 
filtered ether, left to spontaneous evaporation for a day and a night, yielded a large 
quantity of broad silky crystals floating in the liquor, which when viewed through a 
microscope, were found to have exactly the form of cholesterine. Heated upon a 
platina knife, the substance fused and burned with a brilliant flame, like chole- 
sterine, leaving no residue. It had also a light consistence and the pearly lustre of 
cholesterine, was insoluble in water and in cold alcohol, but soluble in hot alcohol. 
From the above results, there is every reason to believe that this substance is chole- 
sterine : this immediate principle of the bile is known, moreover, to exist generally 
