This last statement is absolutely false, as a disease of the eyes may very well exist with a perfect condition of the teeth, and _vice versa_. However, Ryff has the merit of being, perhaps, the first who has noted the undeniable relation which exists between the dental and ocular affections. After a rapid glance at the anatomy and physiology of the teeth, the author enumerates the causes of dental disease, which, according to him, are principally heat, cold, the gathering of humors, and traumatic actions. The prophylaxis of dental diseases is beyond any doubt one of the best parts of the book; however, the ten rules counselled by Ryff for keeping the teeth healthy—rules which Dr. Geist-Jacobi has made known to us in full—are reproduced, almost to a word, from Giovanni d’Arcoli’s work; therefore, the author has no other merit than that of having translated them into the vulgar tongue, thus diffusing the knowledge of useful precepts for preventing dental diseases. We refrain from reproducing the aforesaid rules here, as they are, with slight variations, identical with those which we gave when speaking of Arculanus. Nor can any credit be given to Ryff for the rules which he gives in regard to the diagnosis of dental pains, as this part of his work is also taken wholly from the Italian author just mentioned. After these diagnostic rules Ryff, continuing to translate from the book of Giovanni d’Arcoli, adds: “If the pain comes from the gums, extraction is of no use; if it comes from the tooth, extraction makes it cease; when, lastly, it is in the nerve, sometimes extraction removes it, and sometimes it does not, according as the matter obtains or not a free exit.” The barbers and tooth-drawers, he says, must well remember this rule, in order to avoid extracting, thoughtlessly and with no benefit, sound teeth, since then the pain persists in spite of the operation. Also, it must be borne in mind that, in case of violent pain, it is necessary to operate as soon as possible, so that the patient may not faint or be attacked by the falling sickness, if the pain should be communicated to the heart or brain. The idea that violent dental pains could give rise to syncope or to epilepsy (in regard to which we only observe that even very recent writers enumerate dental caries among the causes of the so-called reflex epilepsy) is also found in Giovanni d’Arcoli, who expresses himself in regard to this in the following terms: “Such very violent pains are sometimes followed by syncope or epilepsy, through injury communicated to the heart or brain.”[279] “The most atrocious pain,” says Ryff, “is when an apostema ripens in the root;” literal translation of words written about a century before by Arculanus: “Fortissima dolor est, qui provenit ab apostemate, quod in radice dentis maturatur.”