OF THE NERVES. It appears from every experiment, which has been made in prosecution of Galvani’s discovery, that the nerves are very essentially concerned, in all the phenomena which it exhibits. It becomes, therefore, an object of inquiry, highly interesting, to ascertain if all the nerves of the body are equally subjects of this new influence, or if its effects are confined to those appropriated to muscles of voluntary motion. With this view, I surrounded with tin-foil the parvagum and intercostal nerves of several cows and sheep, while the auricles of their hearts were still contracting, and placed one end of a bent silver rod, at one time upon the heart itself, at another upon adjacent muscles, and sometimes upon the nerves; but all without producing the slightest perceptible variations, in the contractions of the heart, or a renewal of them when they had ceased. I likewise included the caroted artery in the tin-foil; and, at another time, inserted the foil in longitudinal incisions made in the nerves, that it might be more immediately in contact with their substance; but still no contractions followed. I had as little success when I made similar experiments upon a dog, cats, rabbits, fowls, and frogs; yet, in all these animals, I could in general excite vigorous contractions, by arming the nerves of parts obedient to the will: I say in general, for in rabbits I have sometimes failed altogether; especially when they have been drowned in very cold water. Soon after making these experiments, I perceived from one of Dr Valli’s letters, published in the Journal de Physique, that he had made a similar one upon the heart of a dog, and with the same result. The heart, through the medium of its nerves, is not excitable, therefore, by the same means which are found efficacious in exciting other muscles to contraction. I confess I had not expected this result. It has been asserted indeed, by many physiologists of the first name[11], that the heart can in nowise be affected by the application of a stimulus to its nerves, or to the brain; but many considerations excited my doubts upon this subject, and some experiments which I made at this place, more than a year ago, tended to confirm me in an opposite opinion. That both the frequency, and the strength of the heart’s contractions are affected by passions of the mind, is a fact known to every one; but what is much more to the purpose, since we know so little either of mind or of its mode of influencing the body, we know that many derangements of the brain, such as apoplexy, hydrocephalus, phrenitis, &c. together with all kinds of mechanical injuries, (and what are these, but so many stimuli irritating the brain, and consequently the nerves sent to the heart?) affect the motions of the heart most materially and obviously. The contractions of the heart, so long as the brain remains entire, may be affected by a thousand different substances thrown into the stomach;