a kind of combustion and putrefaction, has had its quality changed to acid. There is no need, however, to dispute about names, but we must realise the facts, which are as follow:-- In the genesis of blood, everything in the nutriment[292] which belongs naturally to the thick and earth-like part of the food,[292] and which does not take on well the alteration produced by the innate heat--all this the spleen draws into itself. On the other hand, that part of the nutriment which is roasted, so to speak, or burnt (this will be the warmest and sweetest part of it, like honey and fat), becomes _yellow bile_, and is cleared away through the so-called biliary[293] vessels; now, this is thin, moist, and fluid, not like what it is when, having been roasted to an _excessive_ degree, it becomes yellow, fiery, and thick, like the yolk of eggs; for this latter is already abnormal, while the previously mentioned state is natural. Similarly with the black humour: that which does not yet produce, as I say, this seething and fermentation on the ground, is natural, while that which has taken over this character and faculty is unnatural; it has assumed an acridity owing to the combustion caused by abnormal heat, and has practically become transformed into ashes.[294] In somewhat the same way burned lees differ from unburned. The former is a warm substance, able to burn, dissolve, and destroy the flesh. The other kind, which has not yet undergone combustion, one may find the physicians employing for the same purposes that one uses the so-called _potter's earth_ and other substances which have naturally a combined drying and chilling action.