Aulus Cornelius Celsus lived in the reigns of Augustus and Tiberius. References in his works show that he either lived at the same time as Themison or shortly after him. Verona has been claimed as his birthplace, but the purity of his literary style shows that he lived for a considerable time in Rome, and he was probably educated there. In Pliny's account of the history of medicine, Celsus is not mentioned as having practised in Rome, and it is almost certain that he combined the practice of medicine with the study of science and literary pursuits; his practice was not general, but restricted to his friends and dependents. His writings show that he had a clinical knowledge of disease and a considerable amount of medical experience. He wrote not only on medicine but also on history, philosophy, jurisprudence and rhetoric, agriculture and military tactics. His great medical work, "De Medicina," comprises eight books. He properly begins with the history of medicine, and then proceeds to discuss the merits of the controversy between the Dogmatici and the Empirici. The first two books deal with general principles and with diet, and the remaining books with particular diseases; the third and fourth with internal diseases, the fifth and sixth with external diseases and pharmacy, and the last two are surgical, and of great merit and importance. In his methods of treatment there can be discerned the influence of Asclepiades of Prusa, and the Hippocratic principle of aiding rather than opposing nature, but some of his work displays originality. His devotion to Hippocrates hindered very much the exercise of his own powers, and set a bad example, in this respect, to his successors. He was rather free in the use of the lancet, but not to the same extent as his contemporaries, and he advocated the use of free purgation as well as bleeding. He never could rid his mind of the orthodox humoral theories of his predecessors. (1) _Surgery._--Although Celsus is the first writer in Rome to deal fully with surgical procedures, it must not be inferred that the practice of this art began to be developed in his time, for surgery was then much more advanced than medicine. Many major operations were performed, and it is very instructive for doctors of the present day to learn that much that is considered modern was well understood by the ancients. There is no greater fallacy than to suppose that medical practice generally, and surgery in particular, has reached no eminence except in very recent times. The operation of crushing a stone in the bladder was devised at Alexandria by Ammonius Lithotomos, (287 B.C.), and is thus described by Celsus:--