Empedocles believes, that animals are nourished by the remaining in them of that which is proper to their own nature; they are augmented by the application of heat; and the subtraction of either of these makes them to languish and decay. The stature of men in this present age, if compared with the magnitude of those men which were first produced, is only a mere infancy. CHAPTER XXVIII. WHENCE IT IS THAT IN ANIMALS THERE ARE APPETITES AND PLEASURES. Empedocles says that the want of those elements which compose animals gives to them appetite, and pleasures spring from humidity. As to the motions of dangers and such like things as perturbations, etc.... CHAPTER XXIX. WHAT IS THE CAUSE OF A FEVER, OR WHETHER IT IS AN AFFECTION OF THE BODY ANNEXED TO A PRIMARY PASSION Erasistratus gives this definition of a fever: A fever is a quick motion of blood, not produced by our consent, which enters into the vessels, the seat of the vital spirits. This we see in the sea; it is in a serene calm when nothing disturbs it, but is in motion when a violent preternatural wind blows upon it, and then it rageth and is circled with waves. After this manner it is in the body of man; when the blood is in a nimble agitation, then it falls upon those vessels in which the spirits are, and there being in an extraordinary heat, it fires the whole body. The opinion that a fever is an appendix to a preceding affection pleaseth him. Diocles proceeds after this manner: Those things which are internal and latent are manifested by those which externally break forth and appear; and it is clear to us that a fever is annexed to certain outward affections, for example, to wounds, inflaming tumors, inguinary abscesses. CHAPTER XXX. OF HEALTH, SICKNESS, AND OLD AGE.