considerations make it certain that Valerius was not the author. [11] Many interesting details were given in it, taken chiefly from Varro; and it is much to be regretted that the entire treatise is not preserved. Besides Paris one Titius Probus retouched the work in a still later age, and a third abstract by Januarius Nepotianus is mentioned. This last writer cut out all the padding which Valerius had so largely used ("_dum se ostentat sententiis, locis iactat, fundit excessibus_"), and reduced the work to a bare skeleton of facts. A much more important writer, one of whose treatises only has reached us, was A. CORNELIUS CELSUS. He stood in the first rank of Roman scientists, was quite encyclopaedic in his learning, and wrote, like Cato, on eloquence, law, farming, medicine, and tactics. There is no doubt that the work on medicine (extending over Books VI.-XIII. of his Encyclopaedia) which we possess, was the best of his writings, but the chapters on agriculture also are highly praised by Columella. At this time, as Des Etangs remarks, nearly all the knowledge and practice of medicine was in the hands of Greek physicians, and these either freedmen or slaves. Roman practitioners seem to have inspired less confidence even when they were willing to study. Habits of scientific observation are hereditary; and for centuries the Greeks had studied the conditions of health and the theory of disease, as well as practised the empirical side of the art, and most Romans were well content to leave the whole in their hands.