It is necessary, as in the preceding case, to distinguish the nutritive phenomena into those which take place before, during and after the cutting. Before the cutting, we observe by opening the jaw, a row of dental follicles, corresponding to the row of teeth already formed, situated below or at the side, and separated from them by little partitions, the thickness of which is found greater in proportion as it is examined nearer infancy. These follicles have precisely the same arrangement as those of the first dentition; like them they form sacs without an opening, the alveolar portion of which is attached, and the loose medullary portion is covered on its surface with the first osseous layers for the crown. The manner of growth is the same; that is to say, it takes place from the exterior to the interior, the reverse of the other bones; an arrangement, which gives the part of the tooth immediately in contact with foreign bodies, being the first formed, time to acquire the solidity necessary for its functions. As the second teeth grow, their vascular system becomes greater, and that of the old ones diminishes; which arises from this, that the sensibility weakened in the last, draws to them no more blood, whilst being raised in the others, it attracts it powerfully. We observe also that the partition of the sockets diminishes in thickness, and that the root of the first is destroyed. This double phenomenon does not appear to be owing to the pressure exerted by the new tooth, as then the root would spread and become flat only; or if it experienced a real destruction, we should find the remains of it, which we never do. It is then probable that, it is by the absorption of the phosphate of lime, that the partition and root disappear, nearly as we have said the internal cavities of the cartilaginous bones are formed. We see from this, that the ossification of the roots of the first teeth is of short duration; it begins the last and terminates the first. When it is of but little extent, the teeth become loose, from the want of insertion. The disappearance of the partitions increases it. It is at about the age of six or seven years that the shedding of them commences; this takes place in the order in which they were cut, that is to say, first the incisors, then the canine, and then the molars. Observe that the last, which appeared at four years of age, are not renewed. _Second Dentition considered at the period of Cutting._