Some historians consider that Celsus was a true doctor by profession; others, instead, hold that he never undertook the cure of the sick. Neither the one nor the other of these opinions is quite acceptable; and it is much more likely, as Daremberg observes in his valuable _Histoire des Sciences Médicales_, that Celsus was one of those philiatri mentioned by Galen, who had studied medicine rather from books than at the bedside of the sick, but who, although not doctors by profession, in case of necessity, put their knowledge and skill into practice on behalf of their relations and friends.[112] The work of Celsus, gathered in great part from Greek authors, has an especial value, because it sums up, in an admirable manner, the whole of the medical and surgical science of the ancients, from the earliest times up to the days of Augustus. The first book of the work _De Medicina_[113] does not contain anything of great importance in regard to dentistry. The following hygienic precept is, however, worthy of note: “After rising, if it be not winter, the mouth should be rinsed with a quantity of fresh water.” In regard to the hygiene of the mouth, nothing more is found in the work of Celsus; and it is also necessary to note that the aforesaid precept forms part of a chapter, in which he speaks of the rules of life, which must be observed by weak people, to which class—the author remarks—belong a greater part of the inhabitants of cities and almost all literary men. According to Celsus, therefore, perfectly healthy and strong people would not even need to wash their mouths with fresh water, and perhaps the keen-witted Roman doctor was not wrong; for it is very probable that the saliva and mucous secretion of the mouth, in perfectly healthy individuals with normal constitutions, have the power of combating the pathogenic germs that produce caries and other diseases of the teeth and mouth. In this way the fact can be explained of many peasants and the greater part of the individuals of the negro race having such good teeth, without possessing even the remotest idea of what hygiene of the mouth may be. And here I venture to refer to a passage in which Celsus alludes to the relation between diseases and civilization with its vices: “It is probable that in ancient times, although there was but little knowledge of medicine, health was for the most part well preserved; this being due to good habits, not yet spoiled by intemperance and idleness. These two vices, first in Greece and then among us, have brought upon us a very host of evils; whence it is that in our days, in spite of the intricate art of medicine—once not necessary to us, as it is not necessary to other peoples—few among us attain the beginning of old age.”[114]