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, 
afer 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 
experiments were not uniform; but in 
several, where every attention to accuracy seems 
_ to have been paid, the irritability of the mus- 
eles 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 
fe fourteen plates. 
ae 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, 
if 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- 
ay motion may recover its irritability by rest, 
_ although all its nerves be divided; 
§ 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. 
4 “ 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- 
bution 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- 
fe 
Vu 
IRRITABILITY. 
and, 
43 
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 
Legallois. ‘Il faut se souvenir que deux faits 
bien constatés ne peuvent jamais s’exclure l’un 
l’autre, et que la contradiction qu’on croit y 
remarquer tient ace qu’il y a entre eux quelque 
intermédiaire, quelque point de contact qui 
nous échappe.” * 
I must here adduce two experiments of my 
own, performed and published many years ago.+ 
“ In an eel, in which the brain had been 
carefully removed, and the spinal marrow de- 
stroyed, the stomach was violently crushed with 
ahammer. 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- 
* CEuvres, Paris, 1824, t.i. p. 21. 
+ See my Essay on the Circulation of the Blood, 
1831, p. 160, 188. 
