IRRITABILITY. 



43 



injury of the limb of the animal as should 

 cause inflammation to succeed the section of 

 the nerves. 



" 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 f<s 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 ; and 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 neivous 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 

 Legallois. " II faut se souvenir que deux fails 

 bien constates ne peuvent jamais s'exclure 1'un 

 1'autre, et que la contradiction qu'on croit y 

 remarquer tient a ce qu'il y a entre eux quelque 

 intermediate, quelque point de contact qui 

 nous echappe." * 



I must here adduce two experiments of my 

 own, performed and published many years ago.f 



" In an eel, in which the brain had been 

 carefully removed, and the spinal marrow de- 

 stroyed, the stomach was violently crushed with 

 a hammer. The heart, which previously beat 

 vigorously sixty times in a minute, stopped 

 suddenly and remained motionless for many 

 seconds. It then contracted ; after a long in- 



* (Euvres, Paris, 1824, t. i. p. 21. 

 t See my Essay on the Circulation of the Blood, 

 1831, p. 160, 188. 



