"With this view, Dr. Reid performed a num ber of experiments on frogs, in which the irrita bility of the muscles of both hind legs was ex hausted or greatly diminished by galvanism, after the nerves of one leg had been divided, and the lower part of the limb rendered per fectly insensible and incapable of voluntary motion, (but without stripping off the skin,) while the nerves of the other had been left entire. The state of the muscles of both limbs was examined after some days. The results of these experiments were not uniform ; but in several, where every attention to accuracy seems to have been paid, the irritability of the mus cles in the palsied limbs appeared to be re stored as perfectly as in others ; contractions being excited in them, in several instances, by the galvanism from four or even two plates, whereas they had formerly been irritated until they were no longer excitable by that from fourteen plates.
" That the muscles which thus recovered their irritability had lost all nervous connexion with the brain or spinal cord was proved, not only by their obvious insensibility, but by after wards cutting off the heads of the animals and forcing a probe along the spinal canal, which excited forcible contractions in all parts, ex cepting the palsied limbs.
" Dr. Alison's paper contained the details of several of these experiments ; and he stated, in conclusion, that as a positive result in such an inquiry must always outweigh a negative one, (particularly where a source of fallacy at tending the latter can be pointed out,) these experiments appear fully to justify the assertion of Dr. Wilson Philip, that a muscle of volun tary motion may recover its irritability by rest, although all its nerves be divided ; and that they afford, perhaps, more direct evidence than any others in support of the doctrine of Haller, now generally admitted in this country, that the property of irritability in muscles is independent of any influence or energy con tinually flowing from the nervous system, although, like every other endowment of living animals, it is subjected to the control of causes which act primarily on that part of the living frame.
" Dr. Allen Thomson expressed a doubt whether these experiments warranted the con clusion drawn from them, not because he ac quiesced in the theory to which they are op posed, nor because he called in question the accuracy of the results described to have been obtained, but because he knew that former ex periments had failed in producing such dimi nution or exhaustion of the irritability of mus cles as had been found by Dr. Reid ; arid con ceived it possible that some of the numerous fallacies to which such experiments are liable might not have been sufficiently guarded against.
" The accuracy of Dr. Reid's statement as to the great diminution or apparent exhaustion of the irritability of the muscles under the in fluence of galvanism, and the subsequent reco very of the power, notwithstanding the division of all their nerves, was satisfactorily established.
It is to be remarked, however, that in these experiments, as usual in such cases, the limbs to which the galvanism was applied were kept moist by the same saline solution with which the galvanic trough was charged ; and Dr. Thomson has observed, that when they are moistened with pure water, the diminution of the irritability under the excitement by galva nism is much less obvious. Hence he was led to suspect that the apparent loss of power in the muscles under that process might depend, not on the circumstance of repeated excitement, but on a degree, however slight, of injury to their texture by the action of the salt. This inquiry he proposes to prosecute further ; but in the meantime it is certain that by the usual process of galvanizing a living muscle moist ened by a saline solution, a very great diminu tion of its irritability may be effected, which may subsequently be regained, notwithstanding the division of all its nerves ; and as the fact of its recovery, not the cause of its diminution or exhaustion, is the point on which the infe rence drawn from these experiments rests, that inference may be held to be sufficiently justi fied." The first question is,—what is the nature of that effect produced upon the nervous and mus cular system by such agents as those employed in these experiments temporarily to diminish or suspend their powers ? The immediate effect of an attack of hemiplegia,the immediate effect of an injury done to the spinal column, by acci dent, or in an experiment, the immediate effect of galvanism, or other stimuli, applied to the nerves or muscles, is to suspend, for a time, the phenomena of the excito-motory power of the nerves, and of the irritability of the muscles, respectively; which, however, repose renews. What is the nature of these changes ? Do they not consist in the sudden reduction and more gradual removal of some physical effect, diffe rent from the diminution and restoration of a purely vital property of these textures, widely different from the slowly induced loss of irrita bility resulting from the removal of its source, the natural physical condition remaining un changed ? At any rate we must agree with Leg,allois. " II faut se souvenir que deux faits bien constates ne peuvent jamais s'exclure l'un l'autre, et que la contradiction qu'on croit y remarquer tient ce qu'il y a entre eux quelque intermediaire, quelque point de contact qui nous echappe."* I must here adduce two experiments of my own, performed and published many years ago.i.