GALEN also states, that in fire there exists a perfect heat and dryness, in earth a perfect coldness and dryness, and so on of the rest of the elements. For you cannot expect to find in nature a perfectly simple and isolated element; because they are always mixed two or more together. Hence the real terram, aquam, aerem, and ignem, become rather a metaphysical abstraction, than a real entity. That is to say, matter has no real existence, but is mere quality; for earth is not the mere representation of dry or siccum; it is the representative of siccitas, or dryness: fire is not the eidolon of calidum, but of caliditas; water of humiditas, and air of frigiditas. Yet all these elements are in nature possessed of more than one property. Fire is hot and dry, earth is dry and cold, water is cold and moist, &c. If we refer, however, to his account of the soul, we perceive at once, that these inseparable qualities of the elements are the real active agents of life. He plainly declares, that the soul is the mere result of organization, and perishes with the structure in which it dwells. He thinks, "corporis temperiem censendum est." As to the active powers of the four primary qualities, he says, "At mihi quidem tam venae, quam reliquarum particularum singulae, ob certam quandam temperiem quam ex quatuor sunt qualitatibus nactae, hoc vel illo modo videntur agere."--De nat. fac. I. It is plain he thinks, that the elements consist of a materia and qualitas; but they are elemental by the _qualitas_ and not by the _materia_. After establishing that there are four elements, which are the common and simple bases of all things, he goes on to show, that the proper proportion and admixture of these, constitute the healthy state of living bodies. If the calidum, for example, be unduly increased, the body is destroyed; if it be improperly diminished by excess of the frigidum, it will also perish. The business of the physician is to keep the proportions just and harmonious; but, as no pure element exists alone, the physician must employ the qualitas in conjunction with the materia. These (to make a phrase) substantive qualities, are found in medicines or food, which, like all objects of sense, are either cold, hot, dry, or moist, and available of course in the management of a cold, hot, dry, or moist derangement of the living body. The elements of the human body exist in the four humours, blood, bile, atrabilis and pituita; and these four humours correspond in quality with the elements. Blood, which is the reservoir or continent of them all, is a temperate humour. Bile, being the representative of calidum, is hot and dry. Melancholy represents, in our microcosm, the element earth or siccum, and is dry and cold. But pituita, which is moist and cold, corresponds with the humidum element. Air exists in animals nearly pure, as we learn from the phenomena of the pulse and of respiration. It answers to frigidum.