Recollecting that fine nervous twigs pass from the ciliary or ophthalmic ganglion, through the sclerotic coat of the eye, to the choroid coat, and to the uvea; and that this ganglion is in great part formed from a twig of the nasal branch, of the fifth pair of nerves, in conjunction with a branch of the third, I proceeded to try if, by insinuating a rod of silver, as far as possible, up my nose, and thus arming this nasal branch, I could, by bringing the silver into contact with a piece of zinc, placed upon my tongue, pass this new influence up the course of the nerve, and thus produce the flash in the eye. The experiment answered my most sanguine expectation. The flash, in this way produced, is, I think, if any thing, stronger than when the ball of the eye itself is armed. I now thought I had discovered a certain method, by which I could ascertain the effect of Galvani’s influence, upon a very important, involuntary muscle, the human iris. It occurred to me that the ingenious physiologist Dr Whytt, had been able, through the medium of the nasal branch of the fifth pair of nerves, to produce, at pleasure, dilatations of the contracted pupil of a boy, in the last stage of hydrocephalus, by applying aq. ammonia to his nostrils; and this instance of the affection, of an involuntary muscle, through the medium of its nerves, had, previously to making any experiments upon the subject, always operated with me as a strong presumptive argument, that the contractions of the heart might be influenced in a similar manner. I therefore desired some of my friends to observe my pupil, while I repeated the experiment, which I have above described. When the external light was strong, they found some difficulty in determining, whether the pupil contracted or not; but when no more light was admitted, than what was just sufficient for discerning the pupil, they perceived a very distinct contraction, every time the metals were brought into contact with each other. This experiment requires some attention, in order that it may succeed satisfactorily; but although I have repeated it a great number of times upon the eyes of others, it has seldom failed, when made in a steady light, and when the silver has been passed far enough up the nose. The dilatation of the pupil, instead of its contraction, on the application of a stimulus to its nerves, as in the case related by Dr Whytt, is, I apprehend, not so uncommon a circumstance, as it may at first be supposed. I have myself seen three instances of it in diseases of the head. One of these was in an epileptic patient, whose pupils, during the intervals of his fits, became suddenly dilated whenever his eyes were exposed to a strong light.