there retained till their mischievous effect is produced.

It is maintained by some writers that caries is contagious. Dr. Koecker was of this opinion. The question, then, is, whether there is any property in the decayed dentine of one tooth capable of producing the same condition in the healthy dentine of another? The residue of dental decay consists of the organic or animal constituents and a small portion of earthy material, and in decay, in which the gelatinous constituent is abstracted, the remainder is chalklike, consisting mainly of phosphate of lime. In neither of these is there anything that can possibly operate on the healthy dentine. There is one thing here, however, that is worthy of remark, and that has perhaps led to the mistaken notion that caries is contagious decayed dentine will absorb and retain fluids that injuriously affect sound dentine, and when the decay is on the proximate portion two teeth are subject to the same exciting cause. But it is seldom that two teeth thus situated are both in the same stage of decay-a fact principally attributable to the difference in their constitution or susceptibility. The decay of the teeth in pairs has also been adduced as evidence of the contagious character of the disease. This, however, results from the fact that the pairs are formed at the same time, are subject to the same influences in their formation, and hence are consti

tuted alike, and if one of the pair is defective, the other will probably be in a like condition. When there is a vitiation of the saliva or mucus they will be similarly affected. In no common acceptation of the term contagious can it be applied to caries of the teeth.

The color of caries is exceedingly various, from that of healthy dentine, through every intermediate shade, to jet black. The rate of the progress is indicated by the color of the decay, being slower as it is darker, so that when the decay becomes almost stationary, the affected portion is usually black. The degrees of color are differently enumerated by different writers, as, by Koecker, five, by others, seven, and so on. Three, however, are sufficient for our purpose: white, brown, and black. The sensitiveness of the dentine is greatest in teeth affected by the white decay, and usually decreases as the color darkens; though there are exceptions to this rule, for occasionally the teeth affected by dark decay are quite sensitive. The light-colored decay is more difficult. to arrest than the dark. In many cases of the former filling seems hardly to retard its progress; whereas, in the latter, by proper filling, the advance of the decay may be checked altogether. The cause of the dark color of caries is mainly due to the carbonization of the animal portion.

The dark, and especially the black variety of decay

is much less rapid in its progress than the light, brown or white variety, and chiefly because the debris or residuum is insoluble, and much less disintegrated than in the other varieties, the animal part being retained in a carbonized state, and the calcareous constituent to a considerable extent retained, and in a form not soluble in the fluids of the mouth.

Thus a far better protection to the dentine beneath is present in the black than in any other variety of decay.

Some sensitiveness commonly accompanies caries. It does not often amount to pain, but is rather a sense of uneasiness; yet, from change of temperature, or contact of acids or hard substances, intense pain may be produced. Dr. Koecker remarks that caries is most tender in its first stages; and Dr. Cone that when a tooth is attacked by it the sensitiveness is increased. The surface of the dentine is susceptible of the most acute sensitiveness. When there is inflammation of the dentine, intense pain may be produced by the contact of an instrument in a cavity of decay, at the line of union of the dentine with the enamel, with very little sensitiveness present elsewhere in the cavity. Sensitiveness of a uniform character sometimes pervades all parts of the cavity, while at other times it may be very intense at one point, and very slight or entirely absent at any other. other. A thin lamina of the dentine lining

the whole cavity may be uniformly sensitive, and in some cases sensitiveness involves the entire body of the dentine.

By means of this sensitiveness, warning is transmitted to the pulp, which emits calcareous material with increased energy; and thus a process of filling up the natural cavity of the tooth is instituted, that the decay may not encroach upon the pulp. But this warning may in some degree be transmitted to the pulp though there be no appreciable increase of sensitiveness.

This sensitiveness is modified by the character of the teeth, the nature of the decay, and the state of the patient's system. The teeth of the same person will be more sensitive at one time than at another, because of a greater irritability of the nervous system. Those teeth which decay most rapidly are usually most sensitive; though in teeth whose vitality is lost considerably in advance of their decay, there is no perceptible sensitiveness present. Except in such cases as last mentioned, the whitest and most rapid decay has most sensitiveness, the brown much less, and the black scarcely any.

PREDISPOSING CAUSES OF CARIES.

The causes of caries of the teeth may be considered under two general divisions-predisposing and excit

ing. Of the former some are original, others accidental. The original development of the constitution may be defective, either from original or from accidental defect in the parent, but more certainly from the former. Constitutional characteristics are transmissible, and a defect is as surely hereditary as anything else. In the foetus, during gestation, germs may have originated from which perfect organs can never be developed, and these germs may be more or less defective according to the constitutional condition of the mother, or according to accidental conditions to which she may be subject, and which may seriously affect the foetus. After birth, too, the child is exposed to injurious impressions, which will, to a greater or less degree, render the development defective; as imperfect nourishment and the diseases and functional derangements peculiar to childhood. A diseased condition, or functional derangement, will interrupt the proper elimination and perfect upbuilding of the materials necessary for the perfect structure; and indeed anything that will disturb the equilibrium of action in the system may be detrimental to the teeth.

In some instances the teeth will exhibit the peculiarities of the mother, and in others those of the father, while sometimes they simulate those of both parents; and when the parental imprint is thus found stamped on the teeth, it will also be found that those