Applied externally lead salts have practically no action upon the unbroken skin, but applied to sores, ulcers or any exposed mucous membranes they coagulate the albumen in the tissues themselves and contract the small vessels.
In virtue of this property they are also mild haemostatics, tending to coagulate the albumens of the blood and thereby to arrest haemorrhage.
The cups when full are poured into a larger vessel, and solution of alum is added to coagulate the latex.
Gallic acid does not coagulate albumen when used externally.
Medicinally, gallic acid has been, and is still, largely used as an astringent, styptic and haemostatic. Gallic acid, however, does not coagulate albumen and therefore possesses no local astringent action.
The latex is therefore usually allowed to coagulate on the tree, as it slowly exudes from the incision.
In some districts the collected milk is heated alone or diluted with water, to coagulate the rubber, but if heated alone an inferior rubber is apt to result owing to overheating.
Externally, it is not absorbed by the unbroken skin, but when applied to the broken skin, sores, ulcers and mucous surfaces, the ferric salts are powerful astringents, because they coagulate the albuminous fluids in the tissues themselves.
Not only does exposure to heat sufficient to coagulate protein matter destroy life, by demolishing Life con- the molecular structure upon which life depends; but ditioned all vital activity, all phenomena of nutritive growth, by tern' movement and reproduction are possible only be- perature.
The acid not only takes up water, but it acts on the suspended impurities, carbonizing them to some extent, and thus causing them to coagulate and fall down in the form of a flocculent mass, which carries with it mechanically other impurities which have not been acted upon.