All the ancient authorities held that a fever consists of a preternatural increase of the Innate, or, as it is now called, Animal heat, which they considered as the instrument by which the soul performs all the functions of the body. See Alexander Aphrod. (de Feb.) Thus, Palladius defines a fever to be “a preternatural heat, which begins in the heart, and is diffused by the arteries over the whole body, sensibly injuring the actions of the body.” Hippocrates, Galen, Aëtius, Alexander Trallian, Psellus, Leo, and Actuarius give similar definitions. Cælius Aurelianus says of Asclepiades: “Febrium ponit signum calorem plurimum.” (Morb. Acut. i, 14.) Isidorus defines a fever thus: “Febris a fervore dicta est; est enim abundantia caloris.” (Orig.) Hippocrates, however, the great opponent of hypothesis in medicine, insists that there is more in a fever than a simple excess of pure heat; or, in other words, that the essence of fever is heat mixed up with noxious qualities. (De Vet. Med. § 17.) The celebrated Erasistratus maintained an opinion, lately revived by Clutterbuck and Broussais, that fevers and inflammations are identical. See Milligan’s Celsus (p. 13 and 112); and Cælius Aurelianus (de Acut. Morb. ii, 3.) He further taught that in fevers the blood of the veins is thrown into the arteries. (Plutarch de Placit. Philos. v, 29.) The Arabians adopt the opinions of Hippocrates, Alexander, and Galen. Thus, for example, Haly Abbas defines fever to be a preternatural heat proceeding from the heart, and diffused by the arteries over all parts of the body. According to him there are three kinds of fevers. The first, are seated in the spirits, and affect only the heat of the body: these are called ephemeral fevers. The second, originate in a vitiated state of the fluids, which impart a preternatural degree of heat to the heart, whence it is diffused over all the body. The third arise in the vital organs and solid parts, from which heat is transmitted to the heart. (Pract. viii, 2.) See also, in particular, Rhases (Cont. xxx.) SECT. II.—OF THE PRINCIPAL CONSIDERATIONS TO BE INQUIRED INTO WITH REGARD TO FEBRILE AFFECTIONS. The first thing to be considered is, whether the disease will prove fatal or not; then, if it is not to prove fatal, whether it will be acute or chronic (these considerations apply to other great disorders); and, third, whether it will come to a crisis all at once (which is peculiar to fevers), or be resolved gradually. * * * * * COMMENTARY. This Section, and great part of the contents of this book are taken from Galen (Therap. ad Glauc. i,) or from Oribasius (Synops. vi.) SECT. III.—FROM GALEN, WHAT TO CALL THE COMMENCEMENT OF THE DISEASE.