On the Termination of the Nerves in the Teeth of Mammalia

No apology is necessary for the reopening of the discussion, time worn though it is, upon the imiode of the final termiiination of the nerve fibres found in the pulps of the teeth of iniainm-ialia, for in spite of all the work that has been done upon this subject by very numerous histologists no solution of the probleml has as yet commllilended itself to the majority. At the present time we find that broadly speaking they miiay be divided into two classes: first, those who think that the fibres after leaving their mnedullary sheaths actuallv enter the dentinal tubules and, running in themii, terminate in the granular laver of Tom-les or at the amiielodentinal junction ; secondly, those wAaho deny that they enter the tubLules but believe that they termiiinate in or around the odontoblast cells. Before, however, we enter upon such an investigation there are certain a priori considerations whiclh have to be clearly understood for an intelligent grasp of the problemii that lies in front of us. The im-ost imiiportant of these is the sensibility of dentine. We as dentists are, alas, only too famiiliar with this, (and there re few, if any, of us who doubt that this is a true sensibilitv and not a mere effect of pressure transmitted mechanically through to a sentient pulp. If any doubt exists it should be cleared by the fact that the sensibility of dentine is greatest at its periphei-y, and that it can be stimiulated by such chemical reagents as dilute acids, e.g., phosphorlic. We miiust all of us have noticed that while the introduction of oxyphosphate cemnent is accompanied by no pain in the mnajority of cases, in those cavities which are very sensitive to excavate, miany of which are very shallow and so less liable to transiit therm-ial changes, such introduction is accom-lpanied by pain of an acute though temporary character. If, then, we turn to physiology for an explanation of this fact we find that so far as is known all sensation in all parts of the body is produced by the direct stimlulation of afferent nerve fibres, and thus by inference we should expect to find nerve fibres in the dentine of humlian teeth at any rate. This is a conclusion that I