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this property distinguishes it from all other animalsubstances.

According to Fourcroy and Vauquelin , 100 partsof urea when distilled yield

92.027 parts of carbonate of ammonia,

4.608 carburetted hydrogene gas.

3.225 of charcoal.

Urea , particularly when mixed with albumen orgelatine, readily undergoes putrefaction.

Uric acid, as has been shewn by Dr. Egan, maybe obtained from human urine by pouring an acidinto it; and it often falls down from urine in theform of brick-coloured crystals. It consists of car-bon, hydrogene, oxygene, and azote: but theirproportions have not yet been determined. Uricacid is one of the animal substances least liable toundergo the process of putrefaction.

According to the different proportions of theseprinciples in animal compounds, so are the changesthey undergo different. When there is much salineor earthy matter mixed or combined with them, theprogress of their decomposition is less rapid thanwhen they are principally composed of fibrine, al-bumen, gelatine, or urea.

The ammonia given off from animal compoundsin putrefaction may be conceived to be formed atthe time of their decomposition by the combinationof hydrogene and azote; except this matter, theother products of putrefaction are analogous to thoseafforded by the fermentation of vegetable sub-