Problemata Aristotelis

Why do freshly removed hides, especially those of rams, applied to the wounds and welts of beatings, and eggs broken over them, prevent ulcers from forming? Is it because, by their nature, both prevent the humor from gathering and swelling? For a bruised part draws humor and swells on account of the heat. Eggs, by their stickiness, glue the skin and thus do not allow it to swell, just as they are used in burns to glue the skin; hides also, by their stickiness, adhere and surely, by their own heat, digest the inflammation and soothe it. We are not accustomed to removing them until some days have passed, even for those who think that rubbing with salt or vinegar will remove the inflammation.

Why do scars, which are black on the rest of the body, appear white on the eyes? Is it because a scar takes on a color contrary to its previous one, just like everything that has been sick? But ulcers on the part of the eye are accustomed to being drawn black. Nevertheless, they do not immediately turn black on the body, but are white at the beginning; nor are they always black on the eye, but eventually turn so, either entirely or in large part.

Why does a rod make the edges or the perimeter of a strike reddish, but the center white? Is it because it pushes the blood from the center, which it strikes most strongly because it gathers itself into a circle and is round? Or is it for that very reason that the blood should then return? Redness, however, is nothing but a confluence of blood, and that into the place where it was struck.

Why, when limbs are struck quite vehemently by a rod, does the center of the flesh turn white, while the edges turn red? But with wood, conversely, the center turns redder. Is it because the rod, due to its lightness, where it has struck vehemently, dissipates the blood resting on the surface? Thus, where blood has been lacking, that part soon appears white. But where it has flowed more fully, this redness surrounds it.