irritation in causing pain. From what I have just said, this may be of two kinds—a reflex or associated pain expressed in some other nerve than the one affected, or else it may be due to direct irritation in the nerve itself. A very common example of the former is seen in the headaches from which many women suffer, from the menstrual congestion (irritation of the nerves) of the ovaries and uterus. It is, however, quite outside the scope of this paper to enlarge on this curious and obscure part of our subject. I prefer to take up the more understood and more common form of direct peripheral irritation, and especially the irritation arising from diseases of the teeth and jaws. In that delightful book, “Rest and Pain,” by Mr. John Hilton, the eminent London surgeon, he narrates a case, which is so instructive in illustrating the mode in which peripheral irritation may cause not only pain, but local disease, that I cannot forbear from quoting it: “A gentleman, aged 63, came to consult me about an ulcer situated upon the left side of his tongue. On examination, I found an elongated, very ugly-looking ulcer, nearly as large as a bitter almond, and of much the same shape. The surrounding parts were swollen, hard, red, and much inflamed, and a lymphatic gland was enlarged below the horizontal ramus of the lower jaw on the same side. I saw in the mouth a rugged tooth, with several projecting points upon it, opposite the ulcer. This gentleman observed to me: “Having suffered a good deal from earache on the left side for a long time, without experiencing any relief from medical treatment, it was thought that I must be gouty, and I went to a surgeon who treats gouty affections of the ear. This surgeon paid great attention to my ear, but certainly did not do it the slightest degree of good. I accidentally mentioned to him that I had for some time past something the matter with my tongue. On seeing it, he immediately began to apply caustic vigorously; moreover, not satisfied with applying it himself, he gave it to my wife that she might apply it at home. I have gone on in this way from day to day, until the pain in my ear is very considerably increased, and the ulcer on my tongue is enlarging; so I have come to you for your opinion regarding my state; for, to tell you the truth, I am afraid of a cancer in my tongue.” I thought I saw the explanation of this patient’s symptoms. The pain in the ear was expressed by the fifth nerve, and there was a rugged tooth with little projections on it, some of which touched a small filament of the lingual-gustatory branch of the fifth nerve in the surface of the ulcer. I detected this little filament by placing upon it the end of a blunt probe. It was situated near the centre of the ulcer, and was by far its most exquisitely painful part. This exposed nerve caused the pain in the auditory canal which led him to go to the aurist, and the aurist, instead of confining himself to his own department, seized the tongue,