We have now briefly reviewed the main forms of peripheral irritation, which act as the efficient causes of dental pain, just as we have glanced over the main constitutional causes that predispose to it. I think you will all agree with me that for the successful treatment of these cases, especially in the chronic and inveterate type, local and constitutional treatment have both to be employed. It seems to me there is great need for the more intelligent co-operation of physicians and dentists to attain the best results. Attention to one side of the question is not sufficient. For the permanent cure of our patients, the treatment of the local mischief has to be supplemented by attention directed to the constitutional conditions that predispose to it. One of the cases I quoted illustrated the important fact that a local irritation may set up a condition of pain in other nerves which the cure of the original lesion entirely failed to relieve. This fact is borne out by many similar conditions which we meet with in other departments of medicine. On the other hand, while a particular attack of pain may be relieved by constitutional remedies, its recurrence can only be prevented by curing the local condition, which acts as the exciting cause. The enormous preponderance of cases of pain of the fifth nerve, compared with other nerves, is to be accounted for by the liability of the delicately adjusted mechanism of the organs supplied to get out of order. This is especially the case with the eye and the teeth. It is beyond the scope of my paper to take up the various constitutional remedies of which we can avail ourselves, rest, the influence of food, the use of the various drugs, the employment of counter-irritation, of electricity, and, lastly, of those surgical procedures, exsection and stretching of painful nerves, which are our last resort. I will more than have attained my object if I have pointed out, however imperfectly, some of the many interesting points at which our respective fields of work touch. Those points where we need your help, and you ours, to accomplish the best results. And now, in conclusion, if we revert to our original question as to what it is that constitutes pain, I think that we will find that both the great authorities I quoted are wrong, and both are right; each has stated half of the truth. If your observation and reasoning agree with mine, we will be forced to believe with Anstie that pain in its essential nature consists in a diminution of the vitality of our central cell, but to further allow with Erb that this is occasioned, or first brought to our notice in most cases, by an increase in the impulses sent to that cell by means of peripheral irritation. BACTERIA, WITH A METHOD OF STAINING FOR DIAGNOSTIC PURPOSES. BY JOSEPH KETCHUM, ESQ. Read and Demonstrated before the Section on Microscopy of the Brooklyn Institute.