ANATOMY. 56c 
blood contained in that cavity, and prefs it towards the 
heart. By too much exercife or abtionthe mufcles them- 
lelves grow hard and tendinous on all Tides ; tliey render 
the parts upon which they arc incumbent cartilaginous, 
or elfe change thole which are membranous into a bony 
nature; they incrcafe the roughnefs, protuberances, and 
procelfes, of.'the bones which lie next to them, and exca¬ 
vate their Hat parts; they dilate the cells of the diploe, 
and incurvate the bones. 
The mufcle which the ftimulus has ceafed to irritate, 
or for the aftion of which the mind has no occalion, is 
relaxed, and grows foft; its wrinkles grow plain ; its fibres 
are rendered longer, receding from the middle towards 
the fixed extremities ; and its fwelling falls. Whatever is 
the caufeof additional contraction is then taken away ; but 
the vis inlita remains. It may be alked, What becomes of 
the fpirit that is lent from the brain-? A part of it perhaps 
exhales; a part of it may be fufpected to adhere to the 
fibre ; and thus it happens that the mufcles grow ftrong 
with ’exercife, and their brawny parts become thicker. 
The three noted dalles of animal powers, elaficity, irri¬ 
tability, and fenjibility, Dr. Wrilberg obferves, have been 
and are yet too much confounded, although it is no diffi¬ 
cult talk to diltinguilh thefe affections from one another. 
The elafticity and cohefion of the fibres, which in different 
degrees are found in every part of the body, was fully 
known to Bellini, Baglivi, Stahl, Pacchioni, Juncker, See. 
That power, known to Stahl’s followers under the appel¬ 
lation of tone, has no fimilarity to irritability, fenfibility, 
and what is called vital power. It either alone performs 
the various actions of the animal and vegetable body, or 
adds ftrength and vigour to them : the former is manifeft 
in the motion of the ribs and cartilages; and the latter in 
the conftrudtion of the uterus, veflels, and membranes. It 
by no means depends on the vital powers, but may endure 
long after death; it is not completely deflroyed even by 
putrefaction. During life it is diminiffied by various caufes, 
and again reftored by feveral remedies. Irritability, which 
Haller thought exilted in the fibres of the mufcles alone, 
and which indeed was known by name, but not in reality, 
to Gliffon, is a kind of animal power, unknown to earlier 
anatomifls, and is different from that power which Hippo¬ 
crates calls evopfjLow. It is proved, from the experiments 
of Lups, Haller, Fontana, Hoffman, and feveral others, 
to differ from elallicity in its rife, duration, feat, caufes, 
effects, and phenomena, r. It is molt powerful in the 
’ mufcular fibres of the whole body, but not equally dif- 
perfed through all; more powerful in the heart, mufcles 
of refpiration, and inteltines, but becomes gradually weak¬ 
er among the voluntary mufcles; and it exilts perhaps, in 
a fmall degree, in the veffels and membranes, as appears 
from the doubts offered by Whyte, De Haen, Van Doe- 
veren, &c. which Haller and the learned Cigna have an- 
fwered. 2. The phenomena of irritability, and the irrita¬ 
tions themfelves by which thefe phenomena are produced, 
are not always tire fame. In lome parts we conltantly per¬ 
ceive a manifeft irritability produced by every irritation, as 
is the cafe in almoff all the mufcles. In many other parts, 
we fee the greateft inconftancy and very irregular effeCts, 
varying differently, at different times, being fometimes in- 
creafed and fometimes diminiffied, at one time yielding to, 
and at another refilling, the irritations; all which is evi¬ 
dent in the (kin, vifeera, veffels, and iris. The learned 
pathologifls, Eller, Tiii'ot, and Gerhard, have long, ago 
acknowledged the great life of the doClrine of irritability. 
It would be of much importance to know the remedies, 
which particularly conduce to excite irritability when it 
is languid, or to diminifii it when it is too great. Opium, 
and the other narcotics, camphor, cantharides, acrid poi- 
fons, bark, the eledfric ffiock, (hew a clear influx of ani¬ 
mal fpirits in the production of irritability. That it is 
different from the fentient faculty, and therefore by no 
means depends upon the nerves, appears partly from other 
reafons, and partly from the irritability of vegetables. 
Though we might take into account fome phenomena of 
Vol. I. No. 36. 
the dionaea mufcipula, according to Ellis’s obfervations, 
or of the hedyfarum or the anthers of certain other plants, 
yet we lhould be averfe to compare this contractile power 
of fome parts of vegetables with irritability; for the in¬ 
ternal tremor of the conftituent parts, which makes the 
particular character of irritability, is wanting in all vege¬ 
tables; we fee contraction and motion alone, which are 
alfo obfervable in other elaftic bodies, where we fuppofe 
no irritability to exifi. The fentient faculty, depending 
folely upon the nerves, although it has been regarded as 
one and the fame thing with irritability, has been more 
■ffrongly oppofed by Haller’s opponents, De Haen, Whyte, 
Le Cat, Gerhard, &c. than irritability fffelf, The fenfi¬ 
bility of the parts is Jo be referred both to the various 
quantity of the nerves, their fituation and date, according 
to Haller’s and Caftell’s experiments, and to the various 
violence of irritation, and the nature of the irritating or 
offending body ; for fome parts are frequently much affec¬ 
ted at one time and lefs at another, and Haller thinks that 
fome of them may fometimes be altogether infenfible. We 
(hall not repeat what has been often offered on the opinion, 
that a greater pain having preceded, abforbs a lefs pain 
following; thus we do not feel the tafte of a drop of wine, 
if we have taken a very fmall quantity of rectified alcohol 
upon the tongue a little before. It cannot however be de¬ 
nied, that, in inflammatory difeafes, affections of the mind, 
and other caufes, it may happen, that hurt parts may feel, 
which, under any other condition, feem infenfible. The 
vital power of certain learned men of later times, as Vanden 
Bos, Bikker, Gaubius, Albinus, See. feenrs rather com¬ 
pounded of all the animal powers comprehended together; 
which opinion, except in fome minutiae, the great Boer- 
haave and Simpfon have more exaCtly adopted. 
Upon the fubjeCt of irritability, and the fentient princi¬ 
ple, as aCting upon the human fibre, Dr. Blane, F.R.S, 
has publiflied fome very pertinent remarks. He contro¬ 
verts the doCirine that all mufcular irritability depends 
upon a fentient principle. “ There have been feveral in- 
ftances (fays he) of the production of feetufes without the 
brain; and a principal faCt in fupport of this opinion is, 
the exiftence of animals without brain or nerves. That 
there are fitch, was firfi obferved by Haller, and has been 
confirmed by Mr. Hunter ; who maintains farther, that 
the ftomach is a centre or feat of life more effential to it 
than the brain. That the ftomach fliotild be an organ of 
fo much confequence, feems natural enough from the im¬ 
portance of its funCfion, which is that of affimilation; and 
life can be more immediately and completely extinguiffied 
by an injury to it, fuch as a blow, than by the fame vio¬ 
lence to any other part of the body. It is alfo well known, 
that the mufcular fibres of animals, endowed with a ner¬ 
vous fyftem, will retain their irritability for fome time 
after their feparation from the brain and nerves. It is 
evident likewife, from the phenomena of vegetation, that 
irritability may exift in nature without fenfation, confci- 
oufnefs, or any fufpicion of the exiftence of a nervous fyf¬ 
tem. In favour of this opinion, it is farther obfervable, 
that thofe animals which are deftitute of brain and nerves 
are of the clafs of vermes, the mod Ample in nature, bavin® - 
only one function, viz. that of affimilation; and therefore 
not requiring that variety of aCtion, and thofe perceptions 
which are peculiar to more complex animals. Laftly, the 
ftate of an egg before incubation, and the condition of 
thofe animals which become torpid from cold, and after¬ 
wards revive, afford faCts which favour this opinion ; as 
they (hew that there is a certain principle of felf-prelerva- 
tion, independent not only of the operation of the nervous 
fyftem, but even of the circulation ; for in this quiefeent 
ftate, thofe portions of animal matter are preferved for a 
great length of time from that corruption to which they 
would otherwife be liable, and their fluids are prevented 
from freezing in a degree of cold which would conceal 
them, were they deftitute of every principle of life.” 
In the courfe of his reasoning, Dr. Blane confiders the 
nervous fyftem not only as a mere appendage to life, but 
7 E as 
