GOTTFRIED BIDLOO, a Dutch anatomist, expresses the idea that the air contributes, after the eruption of the teeth, to hardening them. He did not, however, give any proof of this opinion of his.[364] CLOPTON HAVERS, an Englishman, wrote a book on osteology, by which he acquired great reputation,[365] and in which he treats as well of teeth and their structure. This author believes the enamel of the teeth to be of the nature of stone, and the ivory of the nature of bone. The dental roots, which, he says, are precisely of a bony nature, are covered over with a periosteum, which is in close relation with the gums and with the periosteum of the jaw bone. Clopton Havers held that the dental follicle no longer furnishes any nourishment to the enamel from the moment that this has reached its perfect formation. On the other hand, he assures his readers that he has observed, through the microscope, nervous threads which, departing from the bulb of the tooth, traverse the ivory through small canals, arriving thus at the periosteum. By this anatomical disposition the sensibility of the teeth may, according to him, be explained.[366] Having made this passing allusion to the anatomy of the teeth in the seventeenth century, we will now resume the illustration of those facts relating to the pathological and curative part of the science. WALTER HARRIS, an Englishman, in a pamphlet on acute infantile maladies,[367] recommends again, in cases of difficult dentition, the incision of the gums, a curative practice which had already fallen into disuse.[368] In the authors of that time we find registered a great number of cases of epulis. HIOB VAN MEEKREN speaks of an enormous tumor of the gum that developed in consequence of a traumatic action which had occasioned the loss of a tooth. Before deciding on the extirpation of the tumor, the author thought well to pierce it with a bistoury, to be able to judge whether its ablation might not possibly give rise to a dangerous hemorrhage. The wound having bled but little, he proceeded to operate; but the tumor was so large that it was necessary to remove it in various portions.[369] The same author refers to a case of a soft epulis, bleeding easily, that developed after a badly performed dental extraction. It was to be foreseen that the ablation of such a tumor would give rise to an abundant hemorrhage. This was, however, staunched by simply using astringent powders, without having recourse to the actual cautery, which the operator had held in readiness.[370] DANIEL MAJOR, wishing to remove a large epulis by tying it, was obliged, in order to keep the ligature in position, to pass the thread through a circular incision made at the base of the tumor. He first used a thread of silk, afterward a silver one, and tightened the ligature every day until the epulis fell off.[371]