36 
The same confusion of ideas on the subject 
of the activity of the animal and the irritability 
of the muscular fibre prevails, I believe, 
amongst our own physiologists; at least, in 
conversation with two, who may rank amongst 
the first, I found that they had uniformly con- 
sidered the respiration and the irritability to be 
directly, instead of inversely, proportionate to 
each other. 
That singular and interesting property of the 
lower orders of animals termed tenacity of life 
is, on the other hand, distinctly associated 
with a high degree of irritability of the mus- 
cular fibre. The property may be defined as 
consisting of the power of sustaining the pri- 
vation of respiration, the privation of food, 
various mutilations, divisions, &e. It is greater 
as we descend in the zoological scale. As 
activity depends upon the presence and condi- 
tion of the spino-cerebral masses acted upon 
by arterial blood, tenacity of life depends upon 
the diminution or absence of these masses and 
of this highly arterialized blood, being greatest 
of all in those animals which approach a mere 
muscular structure. Almost the sole vital pro- 
perty then remaining is the irritability; and 
this property does not immediately suffer from 
division. 
It is possible to reduce some of the reptile 
tribes to a state approaching that of animals 
still lower in the scale, by removing, by very 
slow degrees, successive portions of the ner- 
vous masses. This is most readily done in 
animals in which the respiration is already low, 
and the irritability high, as in the feetus, in the 
very young animal, in the reptile, &c., as in 
the experiments of Leyallois,* M. Serres, 
myself, &c. 
There is, even in animals most tenacious of 
life, one kind of mutilation—one kind of in- 
jury not well borne. As the blood is in its 
lowest condition of stimulus, it cannot be 
withdrawn with impunity; even frogs soon 
perish if their blood be allowed to flow. As the 
irritability, on the other hand, is high, certain 
stimuli, as galvanism, slightly elevated tem- 
peratures, &c. are speedily fatal. The batra- 
chia are promptly destroyed by immersion in 
water of a temperature of 108° of Fahr., and 
some fish and crustacea perish in great num- 
bers under the influence of a thunder-storm. 
It is a singular fact, that the fish alone, whose 
food is found amongst animals of a high irrita- 
bility, should possess an electrical organ for 
the destruction of its prey. 
The application of stimulus has uniformly a 
tendency to reduce the degree of irritability. 
The exclusion of all stimuli allows its augmen- 
tation. During active exercise the irritability 
is diminished ; during sleep it is proportionally 
augmented. 
Weare nowled to take another view of this sub- 
ject ofirritability. Whatisitssource? How is it 
renewed when it has been exhausted? These ques- 
tionslead us totake up another of greatinterest, to 
* Experiences sur le Principe de la Vie. 
+ Anatomie Comparée du Cerveau, tome ii. p, 224, 
¢ Essay on the Circulation, chap. iii. § 1. 
IRRITABILITY. 
physicians especially, viz. what is the condition 
of the muscular irritability in those cases it 
which the influence of the cerebrum, or of th 
spinal marrow, or both, isremoved respectively 
e cannot discuss this subject more clear 
than by adducing the following observatior 
read before the Royal Medico-Chirurgic 
Society and published in its Transactions, 
the year 1839. 
The utmost discrepancy of opinion prevai 
amongst physiologists and medical writers wpt 
this subject. Prochaska, Nysten, and Legalloe 
state, that the irritability of the muscular fibi 
remains in paralytic limbs; whilst Profess 
Miiller and Dr. Sticker assert the contrary. 1 
attempt has been made to reconcile a contr 
diction not very honourable to our science. 1 
explain this discrepancy of opinion is one 
the objects of this communication. Te 
The authors to whom I have referred, mish 
by the generic term and idea of paralysis, ha 
not sufficiently distinguished between its d 
ferent species. Yet it will be found, as we pre 
ceed, that this distinction is of the utmost in 
seg aay in the explanation of the phenomer 
n fact, cerebral paralysis, or that which n 
moves the influence of the brain, and spin 
paralysis, or that which removes the influen 
of the spinal marrow, are in totally ; 
conditions in reference to the irritability of @ 
rouscular fibre in the limbs severally affecte 
facts equally obvious in experiments and i 
clinical observations. I must make quot 
tions of some length, for these are necessar 
show the present state of the science. I sha 
then proceed to the detail of my own in 
gations. 
The first distinct notice of this subject whic 
I think it necessary to adduce, is contained” 
the following extract from the Opera Minora ‘4 
Prochaska:* “ Vis nervosa que in nervis 
commercio cum cerebro separatis superest, t 
una alterave musculi contractione, quam im 
tati cient, exhauritur, sed millenis plane coi 
vulsionibus excitandis par est; quod expert 
sum in rana, cui medullam spinalem in dot 
abscidi. Supervixit huic vulneri aliquot « 
bus; interim irritando medulle spinalis pa 
eam, que erat infra sectionem, convulsiones - 
artubus inferioribus excitavi toto tempore, ¢ 
supervixit, plane innumeras; neque extret 
tates inferiores prius mortue sunt, quam fe 
rana; Dein quod vis nervosa in nervis ¢ 
persistere possit citra cerebri auxilium proba 
videntur musculi paralytici, in quorum ner 
ob compressionem aliquam preternaturaler 
tum commercium cum cerebro sublatum € 
nihilominus tamen a stimulo electrice scintil 
longo jam tempore paralytici musculi conv 
Juntur.” 
More detailed remarks were made by Ny; 
and these, from being founded upon very ¢ 
tinct post-mostem experiments on the huma 
subject, have excited more attention. This ce 
lebrated physiologist observes, “ Chez deux 
e 
apoplectiques qui avaient succombé au bout d 
ODD 
Z 
"v 
* Ed. 1800, p. 84. 
