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.