THE EXCREMENTS OF MAN AND ANIMALS. 
271 
oxidation. The sulphur contained in the body is therefore evidently not all oxi- 
dized, and it is not impossible that a large proportion of the sulphur existing in the 
organic compounds of the body may by this means be eliminated from the animal 
economy. 
The precipitate obtained by the addition of milk of lime to the alcoholic extract 
of human evacuations having been thoroughly washed with ether in order to sepa- 
rate the whole of the excretine, still generally yields to water or alcohol, when treated 
with hydrochloric acid, a fatty substance having an acid reaction. The characters 
of this substance, evidently an important constituent of the human evacuations, are 
precisely those of margaric acid ; by combining with the lime added to the alcoholic 
extract, it is precipitated along with the excretine and colouring matter. To obtain 
it, two methods may be employed: — 1st. The lime precipitate, deprived of its excre- 
tine, is mixed with alcohol, and heated on the water-bath with hydrochloric acid 
until the whole is dissolved. The acid fluid, on cooling, deposits a mass of crystals, 
which are collected upon a filter; the filtrate containing the colouring matter, 
which is set free by the action of the acid, has now assumed a dark red appearance. 
2nd. The lime precipitate, deprived of its excretine, is suspended in water and decom- 
posed by hydrochloric acid, with the aid of a gentle heat. By this means it is con- 
verted into chloride of calcium, and the insoluble fatty acid being set free is found 
floating in the liquid. Thus obtained, it has a dirty red colour, and no crystalline 
appearance ; it is next collected upon a filter, and dissolved in hot alcohol ; still it 
does not crystallize on cooling ; but if a small quantity of water be added to the 
solution until a muddiness be induced, and heat again applied, the alcohol on cooling 
will deposit a crystalline substance identical with that obtained by the former process. 
If an excess of water be added, with the application of heat, this same substance is 
deposited in an amorphous form, but maybe again obtained crystallized by the same 
process. 
The fatty acid obtained from the lime precipitate was found to have the following 
properties : — It is soluble in ether and in hot alcohol, but insoluble in cold alcohol ; 
its solution has a distinct acid reaction. When dissolved in hot alcohol, it does not 
precipitate or crystallize on cooling. It is entirely insoluble in water, and precipitated 
if water be added to its alcoholic solution ; by heating the mixture the precipitate 
redissolves, and crystallizes on cooling. In its crystalline state it is colourless, has 
a light consistence and a pearly lustre ; the crystals cannot be distinguished by the 
naked eye, but when examined with a microscope, they exhibit the peculiar structure 
of margaric acid ; some have an arborescent appearance, while others consist of 
round masses of crystals radiating from the centre, their peripheral extremities being 
curved in a peculiar manner, and bearing a striking resemblance to margaric acid. 
If exposed for some time to the air, suspended in water, or in a mixture of water and 
alcohol, their structure becomes indistinct. When heated upon a platina knife they 
fuse, evolve a peculiar smell and thick fumes which burn with a flame, and a 
