Aretæus delivers a most striking description of ardent fevers, which we regret that our limits prevent us from giving at full length. The following are some of the most important symptoms: the heat acrid and subtile, especially in the internal parts, desire of cold air and of cold things, the extremities cold, the pulse dense and small, the eyes clear, bright, and reddish; and, if the fever go on increasing, delirium, oblivion of every thing, lividity of the nails, frequent respiration, profuse perspiration about the forehead and neck, coldness of the body, and at last a complete collapse marked by a return of the powers of reason and certain indications of a prophetic spirit. This is but a meagre outline of his matchless delineation of the phenomena of causus. As all the Greek, Latin, and Arabian writers treat of causus in nearly the same terms as Hippocrates, we shall be very brief in noticing their descriptions. According to Alexander, there are two varieties of causus, the true and the spurious, the former being marked by intense thirst, bilious stools, tongue rough and black; and the latter by the thirst being moderate, the tongue not black, and the stools consisting not of bilious matters, but rather of corrupted food. The former kind is said to be occasioned by a bilious, and the latter by a pituitous humour. Aëtius describes the disease in the same terms as our author. He says that it is produced by putrefaction of yellow bile. Palladius says that ardent fevers are occasioned by an erysipelatous inflammation of the lungs, or by the putrefaction of bilious humours which have become immoderately heated. The Arabians describe it exactly as the Greeks. According to Avicenna, there are two varieties of the disease, the bilious and the pituitous. The inseparable symptoms of the disease are, he says, concealed heat, roughness, and, at last, blackness of the tongue. There is no perspiration until after the crisis. For the most part the heat is not strong in the external parts, but is particularly so in the internal. Rhases states that the ardent fever called καῦσος by the Greeks belongs to the class of tertians, only that in the former the heat is more intense, and the paroxysms do not terminate in a complete intermission of the febrile symptoms. The symptoms, he adds, bear a considerable resemblance to those of the tertian intermittent, but are more strongly marked. According to Alsaharavius, the causus, or ardent fever, is occasioned by heated bile collected in the veins adjoining to the heart, stomach, or liver, and its symptoms resemble those of tertians, but are more intense.