THE EXCREMENTS OF MAN AND ANIMALS. 
273 
to saponification takes place in the intestinal canal, together with the farther 
decomposition of the soap into its acid and base. According to Cl. Bernard, the 
above saponification occurs in the duodenum by the action of the pancreatic juice, 
which converts the neutral fats of the food into an emulsion or state fit to be 
absorbed by the lacteals. If it be considered, moreover, that blood contains free 
fatty acids, a circumstance first shown by Lecanu, and which I have had myself 
an opportunity of verifying in Messrs. Wurtz and Verdeil’s laboratory at Paris, 
perhaps we are entitled to admit that the saponification arising from the action 
of the pancreatic juice upon the neutral fats of food, and the decomposition of the 
soap, both take place in the duodenum, the excess of free fatty acid which escapes 
absorption being carried through the intestinal canal, and expelled with the evacua- 
tions. If a powerful free acid were found to exist in the blood, it might be sup- 
posed that the fatty matters saponified by the pancreatic juice are absorbed, the 
soap decomposed in the circulation, and the excess of free acid which could not be 
assimilated, conveyed into the intestines by the intestinal secretions ; but as the 
blood contains no powerful free acid, being, on the contrary, constantly alkaline, 
this theory cannot be maintained. 
I have not yet been able to ascertain with any degree of certainty whether stearic 
acid be present or not in human evacuations ; but if it be considered that margaric 
acid is habitually found in them, and sometimes even in large quantities, although 
the fats contained in the mutton and beef taken as food were nearly pure stearine, 
and if the transformation of stearic acid into margaric acid must take place some- 
where in the body, human fat consisting mainly of margarine, are we not entitled to 
conclude that this stearine is converted into margaric acid during its passage 
through the intestinal canal ? 
The third substance present in human excrements, which may be obtained from 
the lime precipitate, is the colouring matter. If this precipitate, deprived of its 
excretine, be dissolved in alcohol with hydrochloric acid, a dark port-wine-coloured 
solution is produced, which on cooling deposits margaric acid ; the filtrate contains 
the colouring matter free from this acid. By adding water to the solution, and 
concentrating it on the water-bath, the colouring matter separates in the form of 
flakes floating on the fluid, and leaving a nearly colourless mother-liquor. The 
substance is now collected on a filter, dissolved with hot ether, and the solution 
washed with water in order to remove the last traces of hydrochloric acid. The 
ethereal solution, mixed with water and allowed to evaporate spontaneously, deposits 
the colouring matter in the form of a dark brown or black amorphous substance, 
exactly similar to the colouring matter extracted by Dr. Verdeil from the blood, 
and to that which Dr. Harley has lately obtained from urine, with which it appears 
identical. 
I have already alluded more than once to a precipitate or deposit occurring in the 
alcoholic extract of healthy human evacuations, which appears to be of a very com- 
2 N 
MDCCCLIV. 
