42 >; 
PHYSIOLOGY. 
those in which reside the senses of vision, 
hearing, smell, taste, and feeling, which can 
no longer be excited by habitual stimuli to 
which they have been long accustomed?” 
We find, however, some difficulty in admit- 
ting this principle even with the modification 
proposed. If sensibility becomes in this man- 
ner latent, or we cease to take cognizance of 
such functions as are exercised independantly 
of the will merely by the force of habit, does 
it not follow that the 'origin of these functions, 
at least in their aggregate, would have been 
accompanied bv more sensation than is con- 
sistent with the healthy state? Thus the mo- 
ment an animal became conscious of exist- 
ence, it would be the subject of impression 
sufficiently violent to destroy, or at least to 
derange life. Does it not appear that invo- 
luntary living action results from a principle 
dissimilar to that which is preceded by sensa- 
tion ; and that the sensibility here spoken of is 
a kind of intermediate faculty between that 
which gives sensation and volition, and that 
upon which muscular irritation or contrac- 
tion from stimuli depends? When the gal- 
vanic experimenter excites actions in the 
muscles on the insulated thigh of a frog, it 
cannot be supposed that such actions are at- 
tended by perception (for, as it has been pro- 
perly observed by M. Cuvier, “ it appears 
repugnant to the notions we entertain of self, 
and of the unity of our being, to admit the 
possession of sensation by these fragments”) ; 
although the actions are” excited through the 
medium of nervous excitability, and are of a 
different nature from those which would fol- 
low a mere irritation of the muscular fibre. 
May we not then conclude that the nervous 
organization is endowed with a susceptibility 
independantly of actual, or what M. lliche- 
rand perhaps improperly denominates perci- 
pient, sensibility ; and that it is through the 
medium of this faculty that the incessant and 
unperceived performance of the vital functions 
is accomplished? When the voluntary fa- 
culty ceases to acknowledge its accustomed 
and appropriate stimuli ; when sensation for a 
time is totally suspended, as in apoplexy, or 
in experiments on frogs by pouring opium on 
the brain of these animals ; the functions of vi- 
tality are still preserved by means of the sus- 
ceptibility now alluded to. We have else- 
where endeavoured to prove that convulsive 
agitation, whether taking place in the muscles 
of volition, or in those organs which are inde- 
peudant of the will, results from deficient or 
transient excitement (see Medicine, section 
Nervous Diseases ) ; and such defective ex- 
citement seems to result from an unhealthy 
condition of this nervous susceptibility, which, 
in instances of sudden death produced by an 
abrupt and entire abolition of the sentient and 
loco-motive faculty, for some time longer lin- 
gers in the system, deranged indeed, but not 
yet destroyed, and produces those spasmodic 
motions which are observed in an annual 
body under the circumstances which we are 
now supposing. When, for instance, a do- 
mestic fowl is deprived of life, either by its 
head being severed from its body, or by the 
more common mode of screwing the neck, 
a spasmodic convulsive kind of vellications 
will be observed, and indicate the remains of 
this susceptibility of action, for some time 
after perception or actual sensation is gone. 
If the principle now contended for is admit- 
ted, our compassion for the animal in this 
state would be misapplied ; and it must like- 
wise follow that the notion which has been 
maintained by some is altogether erroneous, 
of death from decapitation being a lingering, 
and therefore cruel, mode of terminating ex- 
istence. In the case, however, of articu- 
lated worms, a like separation of parts does 
not appear to operate the same immediate 
destruction of the sensitive and loco-motive 
faculty ; for as in them there is no single brain, 
but ganglia, as the centres of sensation and 
commencing points of volition. Each part 
of a divided worm is thus a distinct living 
and sentient being. From the remains of 
this principle of susceptibility may originate 
those convulsive affections which almost 
invariably precede death in the course of 
nature, and which are oftentimes exhibited 
in a violent degree for some time posterior to 
the departure of the sentient or perceiving 
faculty ; but which last is itself destroyed prior 
to the total destruction of muscular irritability, 
or the vis insita of Haller. This last (Hal- 
lerian irritability) is denominated by modern 
physiologists, contractility. As actual sen- 
sation is demonstrably produced through the 
medium of nerve, so “ the general organ of 
motion is the fleshy or muscular fibre. This 
fibre contracts itself by volition, but the will 
only exercises this power through the medium 
of the nerves. Every fleshy fibre receives a 
nervous filament, and the obedience of the 
fibre ceases when the communication of that 
filament with the rest of the system is inter- 
rupted. Certain external agents applied im- 
mediately to the fibre likewise cause contrac- 
tions, and they preserve their action upon it 
even after the section of its nerve, or its total 
separation from the body, during a period 
which is longer or shorter in different species 
of animals. This faculty of the fibre is called 
its irritability. Does it in the latter case de- 
pend upon the portion of the nerve remain- 
ing in the fibre after its section, which always 
forms an essential part of it? or is the influ- 
ence of the will only a particular circum- 
stance, and the effect of an irritating action of 
the nerve on a faculty inherent in the muscu- 
lar fibre ? Haller and his followers have 
adopted the latter opinion; but every day 
seems to add to the probability of the oppo- 
site theory.” — Cuvier’s Comparative Ana- 
tomy. 
If, however, we resort to analogy, which, in 
the present state of our knowledge with re- 
spect to the composition of muscular fibre, is 
all the aid with which we are furnished to 
solve the question of distinct or separate resi- 
dences of nervous and muscular power, we 
should perhaps be compelled to revert to 
something like the Hallerian doctrine of a vis 
insita, or independant excitability, and con- 
clude that the nerves are merely instruments 
by which the faculty of contractility is deve- 
loped, and that this faculty may otherwise be 
produced by extraneous stimuli, without the 
interference of the nerves. Many plants are 
possessed of contractile, although not (as it ap- 
pears) of actually sensitive and loco-motive 
power: this contractility, from the mode of its 
excitation, and from the phenomena which it 
exhibits, seems in everyway similar to the ir- 
ritability of the animal fibre, nevertheless nei- 
ther brain nor nerves have hitherto been detect- 
ed in vegetables. The attempts to prove that 
irritability and sensibility are one, seem to 
proceed from the general tendency observed 
in the philosophy of the present period, to 
strain the analogy between vegetable and 
animal life. M. * Delametherie, a French 
physiologist, carries this doctrine to the ex- 
tent of denying the existence in toto of any 
distinct muscular fibre. r J he substance which 
has been ordinarily considered to be muscle, 
he considers as “ a' congeries of blood-vessels, 
lymphatics, and nervous filaments, bound to- 
gether by cellular membrane, in the inter- 
stices of which are deposited animal gelatine 
anti tat.” Considerations sur les Etres organi- 
ses, &c. 
It appears to us, however, that sensibility 
and irritability, although intimately connect- 
ed, and never separate in a living animal body, 
areyet distinct principles; at least, that mpre 
and stronger facts than have hitherto been 
advanced, are requisite to the lull establish- 
ment of the modern doctrine, “ that thev 
are in effect the same property.” 
Irritability, or the-power of contraction upon 
the application of stimuli, has been divided 
into two species ; the one has been named 
by some physiologists the tonic power, the 
other musculosity : this difference, however, 
rather refers to the difference* of exciting 
power, by which is called into action the one 
and the other ; the slow, gradual, and tonic- 
like action of the bladder in expelling the 
urine,” seems principally to vary from that, 
of the voluntary muscles by being more 
beyond the inlluence and caprices of the 
will. 
The most remarkable characteristic both 
of sensibility and irritability (forming toge- 
ther vital excitability) is, that as they are sub- 
servient to different purposes, and resident 
in various organs, they are susceptible of de- 
velopement or excitation, by peculiar and 
respective agents. Thus light is a stimulus 
to the eye, sound to the ear, a sapid sub- 
stance to the taste, and an odoriferous body 
the smell. Thus mercury will stimulate 
the hepatic, foxglove the renal viscus, al- 
though in each instance the indivisible facul- 
ties of sensibility or- irritability are called 
into play ; and no difference indicating pe- 
culiar excitability can be traced by the ana- 
tomist in the arrangement, or the chemist in 
the composition, of the ultimate fibrillae con- 
stituting either the nerves or the contractile 
organs of these respective parts. 
The animal frame is thus supported in the 
same manner as a piece ot complicated 
machinery, composed of several springs, 
each of which is kept in exercise by a prin- 
ciple peculiar to itself, while the combined 
effect of them all is one resulting whole, 
effected by one prime, and operating prin- 
ciple ; this, in the living machine, is named 
the vital principle, of which we are now to 
speak. 
Researches into the nature and cause of 
living actions, appear to have been impeded 
by errors arising from different, and in one 
sense, opposite sources ; the one of old, the 
other of modern date. The earliest philo- 
sophers could not have been long in ob- 
serving, while contemplating the phenomena 
of life, “ that it exhibits an order of truths 
peculiar to itself, which is no where to be 
found beyond the sphere of living existence.” 
(Dumas.) Before the proper boundaries 
were discovered of human research, and 
the true nature of philosophizing ascertained. 
