no such income in Gaul. This immunity applied only to mistakes made in the treatment of free men. By chance a law existed at Rome, the Lex Aquilia, passed about 286 BC, which allowed the owners of slaves and animals to seek remedies for damage to their property, either malicious or negligent. Litigants used this law to proceed against the negligence of medici, such as the performance of an operation on a slave by an untrained surgeon resulting in death or other damage. Social position While encouraging and supporting the public and private practice of medicine, the Roman government tended to suppress organizations of medici in society. The constitution provided for the formation of occupational collegia, or guilds. The consuls and the emperors treated these ambivalently. Sometimes they were permitted; more often they were made illegal and were suppressed. The medici formed collegia, which had their own centers, the Scholae Medicorum, but they never amounted to a significant social force. They were regarded as subversive along with all the other collegia. Doctors were nevertheless influential. They liked to write. Compared to the number of books written, not many have survived; for example, Tiberius Claudius Menecrates composed 150 medical works, of which only a few fragments remain. Some that did remain almost in entirety are the works of Galen, Celsus, Hippocrates and the herbal expert, Pedanius Dioscorides who wrote the 5-volume De materia medica. The Natural History of Pliny the Elder became a paradigm for all subsequent works like it and gave its name to the topic, although Pliny was not himself an observer of the natural world like Aristotle or Theophrastus, whose Enquiry into Plants included a book on their medicinal uses. Military medical corps Republican The state of the military medical corps before Augustus is unclear. Corpsmen certainly existed at least for the administration of first aid and were enlisted soldiers rather than civilians. The commander of the legion was held responsible for removing the wounded from the field and insuring that they got sufficient care and time to recover. He could quarter troops in private domiciles if he thought necessary. Authors who have written of Roman military activities before Augustus, such as Livy, mention that wounded troops retired to population centers to recover. Imperial The army of the early empire was sharply and qualitatively different. Augustus defined a permanent professional army by setting the enlistment at 16 years