Numerous reports have now been made of those who have died in consequence of this poison, and the most striking effects to be observed are, the extraordinary state of the eye, which has indeed been considered as the most characteristic phenomenon, and at once to point out the cause of death: the shining, glistening, sparkling lustre of the eye has been, on most occasions, observed. No one has, so far as I am able to learn, attempted to explain this most striking appearance; it has, however, been said, that those who die from the effects of charcoal often exhibit the same unearthly lustre.--_Dr. Sigmond on Poisoning with Prussic Acid.--The Lancet, August 26th, 1837, page 797._ My first experiment was undertaken in 1837, with the diluted acid, by dipping a sponge into it, and rubbing it upon the forehead for the space of a few minutes, which gave the skin a very red appearance; but the patient experienced not the least sense of heat, and the pupil was slightly dilated. I continued to use this with very beneficial effects in incipient cataract, opacities of the cornea, inflammation, amaurosis, iritis, &c. Of late, instead of the diluted acid I have applied the _vapour_ of the concentrated acid to the eye with much more decided effect, and without the slightest danger. The plan I generally adopt, is to put into an ounce-phial a drachm of the acid, and hold it in close contact with the eye, the eyelid being open, for the space of about half a minute, or until such time as the patient feels a little warmth, or the person holding the phial sees the pupil greatly dilated, and the vessels of the eye injected with blood, which is the invariable effect of the application of the acid. The patient is not sensible of pain from this peculiar state being induced, which appears to me to result from the powerfully sedative influence of the acid,[2] thereby showing that two opposite powers--to wit, the stimulating and the sedative--are exerted at the same time; and thereby the uneasiness arising generally from a stimulant alone is prevented. Its great power in removing these diseases chiefly arises from the two powers being so blended, and thus enabling the eye to bear a sufficient stimulating action without injury. The person who holds the acid to the eye should _be careful not to allow the patient to smell it_. [2] _Lancet, Sept. 16th, 1837, page 883._--In whatever manner it is prescribed or administered, either therapeutically or as a poison, hydrocyanic acid operates directly on the nervous centres.--_Professor A. T. Thompson._ The _Medical Gazette_ and the _Lancet_ gave insertion to the following statement of mine, of date Oct. 20, 1842. SIR,--In October, 1841, I gave an account of the action of the vapour of _hydrocyanic acid_ upon diseases of the eye. Since that period I have been engaged in investigating the action of various other bodies on the same organ, and under the same form.