Gout and rheumatism were formerly ascribed a much more important role in the production of pain than they now occupy. Leaving out of account the acute manifestations of these diseases, their influence is slight as predisposing causes in the production at least of facial pain. There is perhaps one disease of the dental apparatus to which I shall allude later on, in which gout may act as an efficient cause. On the other hand, the class of pains due to the action of the chronic abuse of certain therapeutic agents is unhappily an increasing one; I allude to alcohol, opium, cocaine, chloral and other drugs, originally taken for the relief of pain, which induce a pernicious habit in their unfortunate victims, of which pain is one of the main expressions. It is an undoubted fact that this class of sufferers is on the increase. Much of this tendency is due to the excessive wear and tear and the unhealthy competition of our modern civilization. It has always been the refuge of the weak, the attempt to escape from the moral evils of our lot by means of something that will temporarily dull our consciousness of the trials we have gone through and the apparently greater trials that lie ahead of us. The moment the competition for existence and for wealth becomes keener, the greater will be the temptation of the unsuccessful or depraved to seek oblivion for their failure in some narcotic, which will for the time being quiet their disappointed consciousness. When in addition you have an inherited weakness on the part of your patient in his susceptibility to pain, or in a condition of pain actually existing, can you wonder that so many fall by the way? It seems to me that a terrible responsibility lies upon us all, especially upon us physicians, lest by our treatment we encourage this tendency. Nor do I think that as a profession we can be altogether acquitted of carelessness, to put it mildly, in this regard. It is so much easier to relieve the symptom pain, when called to a sufferer, by a dose of morphine, and then when the next attack comes on to repeat it, than to analyze the complex group of phenomena on which that pain depends. You will perceive that the question with which we started as to the nature of pain is of vital importance in this regard. The last group of constitutional agents which act as pain disposers is one with which you are all familiar, namely, the action of certain metallic poisons; of these the most important are mercury and phosphorus. It is highly significant that they have their main action in the structural changes they cause in the periosteum of bones, the peridental membranes.