Timaeus

For when all the substances become reversed and corrupted, they begin by destroying the blood itself, and then they themselves cease to supply any nourishment to the body; for they move through the veins in all directions and no longer preserve the order of their natural revolutions, being at enmity with themselves because they have no enjoyment of themselves, and being at war also with the established and regular constitution of the body, which they corrupt and dissolve. Therefore all the oldest part of the flesh that is decomposed becomes tough and is blackened by the continued combustion; and because it is eaten away on every side it is bitter, and therefore dangerous in its attack on any part of the body that is not as yet corrupted. And at one time the black matter acquires a sharpness in place of its bitterness, when the bitter substance becomes more diluted; and at another time the bitter substance acquires a redder color through being dipped in blood, while if the black matter is blended with this it turns greenish; and again, whenever new flesh also is decomposed by the fire of the inflammation, a yellow matter is commingled with the bitter substance. To all these humors the general designation bile has been given, either by certain physicians or by someone who was capable of surveying a number of dissimilar cases and discerning amongst them one single type worthy to give its name to them all. All the rest that are counted as species of bile have gained their special descriptions in each case from their colors. Serum is of two kinds: one is the mild whey of the blood; the other, being derived from black and acid bile, is malignant whenever it is imbued with a saline quality through the action of heat; and this kind is termed acid phlegm. Another kind involves air and is produced by dissolution from new and tender flesh. And when this is inflated and enclosed by a fluid, and when as a result of this process bubbles are formed which individually are invisible because of their small size but in the aggregate form a mass which is visible, and which possess a color which appears white owing to the foam created,—then we describe all this decomposition of tender flesh intermixed with air as white phlegm. And the whey of phlegm that is newly formed is sweat and tears, and all other such humors as pour forth in the daily purgings of the body. And all these are factors in disease, whenever the blood is not replenished naturally from meats and drinks but receives its mass from opposite substances contrary to Nature’s laws.