Caelius Aurelianus probably flourished during the third century A. D. The different authorities, however, do not agree as to the limits of the period during which he lived; some saying that his career antedated that of Galen, while others claim that he came upon the scene after the death of the latter, which occurred early in the third century A. D. His chief merit appears to have been that, through his translation of the writings of Soranus into Latin, he placed within reach of the physicians of Rome the teachings of that admirable diagnostician and therapeutist; for it must be remembered that the great majority of the Roman medical men were not able to read Greek. On the other hand, Caelius Aurelianus, who was himself a thoroughly practical physician, deserves considerable credit for having enriched the text of his book with many very appropriate examples (chiefly with regard to questions of diagnosis) drawn from his own personal experience, which must have been extensive. During the Middle Ages, as we are informed by Friedlaender, this work furnished the chief source from which the monks derived their knowledge about diseases and their proper treatment. The Latin in which the book is written is described by nearly all the authorities as barbaric. _The Pneumatists._--Methodism had been established only a very few years when Athenaeus of Attalia, a city on the coast of Pamphylia, Asia Minor, founded (about 50 A. D.) a new sect--that of “Pneumatism.” He was not the discoverer of the “pneuma” or “vital spirit,” for that had already been admitted by the earlier schools of philosophy as a fifth primary creative element, supplementary to the four well-known substances--fire, air, earth and water. He believed that heat, cold, moisture and dryness (the primary qualities of these four bodies) were not the veritable elements of living beings. Heat and cold, he maintained, were “efficient causes” and moisture and dryness “material causes.” To these he added “spirit” as a fifth element; and he taught that this spirit enters into the formation of all bodies and preserves them in what may be termed their natural state. It was from the Stoics, more particularly, that Athenaeus borrowed this belief, and it was the latter fact, as Le Clerc says, which led Galen to speak of Chrysippus--one of the most famous of the Stoics--as “the Father of the Sect of the Pneumatists.” In his application of the doctrine of Pneumatism to the science of medicine, Athenaeus maintained that the majority of diseases owed their origin to some disturbance or disorder of the spirit; but it is almost impossible to understand, from the scanty data which have come down to us, what Athenaeus really meant by the term “spirit,” and by the expression “disorder of the spirit.”