I shall also ask permission to change the subject of my remarks from the announced title to one of a little wider scope, namely, Pain, with special reference to its dental relations. I presume the symptom of pain is the one for which the overwhelming number of your patients, as the majority of ours, apply to us for relief. And yet common as this sensation is both in ourselves and in others, it is very remarkable how little settled opinion is, as to its nature. If you have never had occasion to try and put into the form of a definition the idea of pain, and proceed to consult the authorities, you will be surprised that so many different views could be held of what at first seems so common and obvious as to be beyond dispute. As you proceed in your inquiries, the question instead of becoming simpler apparently becomes more complex, for as you think of the different forms of pain, and contrast, for instance, that of an inflamed rheumatic joint, with its definite structural changes and well-marked constitutional symptoms like fever, with an idiopathic neuralgia, pure and simple, often lacking in any outward manifestation other than the pain itself, you wonder if the pains resulting are not as different as the diseases producing them. But the common consciousness of mankind which has given the same name to the sensation produced, whether by an inflamed bowel or a carious tooth, is sure to be right in believing that there is essentially the same substratum in each. Now what is the nature of that substratum? It is evident that whatever else it is, pain is a disagreeable sensation, and the word sensation further obliges us to remember that it involves a central nervous system (in its simplest type a single cell), capable of feeling impulses, conveyed to it from without, or else generated within itself. Now, it is very evident that pain must consist either in some change in the nature of the impulses sent to our central cell, or else in some change in the condition of the receiving centre. So eminent an authority as Prof. Erb defines pain simply as an increase in the ordinary sensory stimulus, a heightening more or less intense of ordinary sensation. On the other hand, Anstie defines pain as a perturbation in the nervous system, especially of the central cells, involving a lowering of function, a diminution of ordinary sensation. It is very evident that both of these great authorities cannot be exclusively right, and I propose to see what light we could get on this subject from the abundant clinical evidence you have. This question is no mere quibble about words or definitions, but it is one of the utmost practical importance in its relation to treatment. According as we settle in our minds whether a given case of pain is an exaggeration or a lessening of the ordinary physiological condition, our treatment will logically be either narcotic or stimulant.