W. M., a house painter, of extremely dissipated habits, but who had never suffered either from distinct symptoms of alcoholism, nor from any affection traceable to lead-poisoning. In March, 1867, he applied to me on account of neuralgic pain, affecting chiefly the right eyeball, but also darting along the course of the frontal nerve of that side; after a short time it extended also into the infra-orbital nerves. He bore several scars of tertiary ulcers about the nose and forehead, and made no secret of having suffered from chancre six or seven years before, and from subsequent secondary and tertiary symptoms. I was consequently not at all surprised at his developing severe iritis (right) after he had been a fortnight under my care, although I had from the first given large doses of iodide of potassium; but I was not prepared for the extensive processes of destruction which followed, notwithstanding that I immediately commenced mercurial treatment, and applied atropine. I remarked that while the inflammation of the iris proceeded with great violence, the cornea was also much more severely affected than is usually the case in syphilitic iritis; in fact, the changes closely resembled those which have been noted after section of the fifth at the Gasserian ganglion, and at the date of the patient's death (seventeen days from the commencement of the iritis) a corneal ulcer was on the point of perforating. For the first three or four days after the iritis set in, the neuralgic pains went on augmenting in intensity, and extended into all three divisions of the fifth; there was a copious discharge from the right nostril. Almost suddenly, on the fourth day, the pains abated and then ceased, and it was now evident that the whole surface of the right half of the face was completely anæsthetic. Two days later a dark-red patch appeared on the cheek, and in the course of the next two days this ulcerated, the ulcer presenting a somewhat livid appearance, and exuding a sanious discharge; at the same time, superficial ulcers appeared on the right side of the tongue, and coalesced to form one large sore. The sores both on cheek and tongue assumed more and more a gangrenous appearance, and on the sixteenth day from the commencement of iritis there was considerable loss of substance in both these situations. On the evening of this day (the patient having become extremely depressed and much emaciated) general epileptiform convulsions set in, and followed each other rapidly; in a few hours coma supervened, and the patient sank the next day. No _post mortem_ could be obtained; but it seems extremely probable, from the above history, that the Gasserian ganglion was early involved in the syphilitic inflammation, and that the neuralgia and subsequent anæsthesia, the iritis, and the other trophic lesions, were due to the injury inflicted upon it.