But in addition to his purely anatomical observations, this author also merits our consideration from the point of view of pathology. He confirmed a most important fact to which allusion had already been made by preceding authors, that is, the atrophy of the alveolar parietes as following on the extraction or on the falling out of teeth. Ruysch, however, makes the observation that atrophy of the alveolar parietes may also precede the falling out of the teeth, and rather be the cause than an effect of it. In such cases the teeth, before falling out, always become more and more loosened, proportionately to the atrophic process. This pathological condition, against which none of the astringent remedies habitually used are of avail, is mostly considered, says Ruysch, to be owing to scurvy; but, he adds, the accumulation of tartar may also be the cause of it. Substantially, Ruysch affirms the relation existing between the accumulations of tartar and the production of that very frequent disease that was afterward named expulsive periodontitis or alveolar pyorrhea. This author also relates two cases of polypous affection of the maxillary sinus. In one of these cases, the existence of a polypus in the maxillary sinus was determined by Ruysch while dissecting a corpse. The other case relates to a female patient upon whom two surgeons had performed the extraction of several molar teeth and the extirpation of an epulis believed by them to be of a malignant character. After the operation they cauterized the diseased part to a great depth with a red-hot iron, reaching as far as the maxillary sinus, which remained open, and from which Ruysch afterward extracted with his little finger several polypi.[357] ANTONI VAN LEEUWENHOEK (1632 to 1723), like the preceding author, a Dutchman, was the first maker of powerful microscopes, by means of which he made many important discoveries; among others, that of the tubular structure of the dentine or tooth bone. This discovery he made known and demonstrated in the year 1678, before the Royal Society in London. In his description of the structure of the teeth, Leeuwenhoek says that 600 to 700 of the dentinal tubuli have hardly the consistence of one hair of a beard.[358] In the year 1683 he discovered in the tartar scraped from between the teeth a form of microörganism upon which he laid special stress. This observation he embodied in the form of a contribution which was presented to the Royal Society of London on September 14, 1683. This paper is of particular importance, not only because of the careful, objective nature of the description given of the bodies seen by him, but also for the illustrations which accompany it. From a perusal of the text and an inspection of the plates, there remains little room for doubt that the bodies described by Leeuwenhoek were not animalcules, as he believed, but bacteria.[359]