M. Vitruvius per Iocundum solito castigatior factus cum figuris et tabula ut iam legi et intelligi possit

...from certain parts of the sky, when it settles into open veins more than the natural temperature of the body can bear. Likewise, if moisture has occupied the veins of the bodies and made them unequal, the other principles, as if corrupted by liquid, are diluted and the virtues of the composition are dissolved. Likewise, from the cooling of moisture, winds, and breezes, vices are poured into the bodies. No less, the natural composition of the air and also the earth in the body, by increasing or decreasing, weakens the other principles: the earth, by the fullness of food; the air, by the heaviness of the sky. But if anyone wishes to perceive these things more diligently by sense, let him observe and attend to the natures of birds, fish, and terrestrial animals, and thus he will consider the differences of temperature. For one genus of birds has one mixture, fish another, and the nature of terrestrial animals is far different. Birds have less earth, less moisture, are tempered by heat, and have much air. Therefore, composed of lighter principles, they strive more easily into the impetus of the air. The aquatic natures of fish, however, which are tempered by heat and are composed mostly of air and earth, have but a very little moisture; the less they have of the principles of moisture in their body, the more easily they endure in moisture. Therefore, when they are brought to land, they leave their life with the water. Likewise, terrestrial animals, which are tempered by principles of air and heat and have less earth and the most moisture—since humid parts abound—cannot maintain life in water for long. Therefore, if these things seem as we have proposed, and we perceive by sense that the bodies of animals are composed from these principles, and we have indicated that they suffer from and are dissolved by excesses or deficiencies, we do not doubt that it is necessary to seek more diligently to choose the most temperate regions of the sky when salubrity must be sought in the placement of walls. Therefore, I also think that the reasoning of the ancients must be recalled again and again. For the elders used to inspect the livers of the cattle that were sacrificed in those places where towns or permanent camps were to be established; and if they were livid and faulty at first, they sacrificed others, doubting whether they were damaged by disease or by the fault of the fodder. When they had tested with many and had proven the whole and solid nature of the livers from the water and fodder, they established fortifications there. But if they found them faulty, they moved elsewhere, a sign that in those places, the supply of water and food would be pestilent to human bodies in the future; and thus they migrated and changed regions, seeking salubrity in all things. That this happens, so that the salubrious properties of the earth may be seen in fodder and food, can be observed and known from the fields of the Cretans: which are around the Pothereus river, which is in Crete between the two cities of Gnoson and Cortyna. For on the right and left of that river, cattle graze: but of those that graze near Gnoson, they have a spleen; but those from the other part, near Cortyna, do not have an apparent spleen.