404 DE. MAECET OIS" THE EVIMEDIATE PEIXCIPLES OE HEAIA^' EXCEEMEXTS. 
substance insoluble in boiling alcohol and remaining on the filter was now submitted to 
examination; the original alcoholic extract ha-ving filtered nearly quite clear through 
the cahco, it was evident that this deposit could consist but in small quantity of insoluble 
substances, which might have found their way through the meshes of the cloth. The 
deposit, removed from the filter into a capsule, was boiled with a solution of caustic 
potash, when the greatest part of it dissolved ; an attempt to filter the fiuid having failed, 
I decomposed the alkaline solution with hydrochloric acid, which induced the formation 
of a precipitate. The precipitate, collected on a filter, was washed with water until the 
washings ceased to exhibit an acid reaction and induce a cloudiness in a solution of 
nitrate of silver. Boiling alcohol and ether dissolved the substance on the filter, it cn’- 
stalhzed on cooling from its solution in alcohol, and by spontaneous evaporation from its 
solution in ether ; by means of repeated crystalhzations in a mixtui-e of alcohol and ether, 
the substance in question was obtained perfectly colourless and pure. ^^Tien heated on a 
platina spatula, it fused and then bmmt with a flame ; a carbonaceous residue was left, 
which, on the further application of heat, disappeared completely, lea'sing no ashes on 
the spatula. When viewed with the microscope, the crystals had the peculiar stellate 
structure of margaric acid ; the substance, when fused and allowed to cool, assumed a 
crystallized nature ; it was found to fuse at 60° Centigrade. The above characters are 
those of margaric acid*, so that this fatty acid is constantly present in healthy human 
evacuations f. 
It was now of much importance to ascertain in which form the margaric acid formd 
in the above circumstances existed as a constituent of human faeces, or in other words, 
to determine the Immediate Principle containing the fatty acid in question ; but pre- 
vious to entering on this subject, I beg to relate an experiment instituted for the pur- 
pose of detecting the best method to be employed to prepare the alcoholic extract of 
excrements. It was noticed that the quantity of the deposit rielded by the extract, on 
cooling, varied according to the manipulations adopted to prepare the solution ; conse- 
quently a healthy and fresh evacuation was tritm-ated in a mortar, in order that every 
part of it should be equally moistened, and the mass was dirided into thi’ee quantities, 
weighing each 60 grammes. Each portion was boiled foiu times successively with two 
ounces of alcohol ; the first part being treated with alcohol in an open tm capsule and 
strained through a clean laboratory towel, the second being boiled in a long-necked flask 
and strained through the same towel, and the third being treated in a similar flask and 
strained through muslin folded in two. The fluid passed very fr’eely tlu’ough the niushn, 
and there appeared to be a greater deposit on cooling in the alcoholic extract of the 
third portion than in that of the two others ; about two hoiu's afteiwai’ds the alcoholic 
extracts were filtered separately through filtering-paper, and a clear dark-coloimed solu- 
* Notwithstanding the fusing-point and crystalline stmctui’e of this fatty acid, it might have been mixed 
with a small proportion of stearic acid and traces of oleic acid. Stearic and mai’garic acid have the same 
chemical properties. 
t I had shown in my previous communication that margaric acid was occasionally present in feces. 
