341 
PHYSIOLOGY. 
of thefe has a different character in the animal and 
organic lives. In the latter, fenfibility is only the capabi¬ 
lity of receivinganimpreflion: in the former,it is the capabi¬ 
lity of receiving an impreffion, with the additional power 
of referring it to a common centre, or confcioufnefs. 
The ftomach is fenfible to the prefence of food, the heart 
to that of the blood, and an excretory tube to the contadl 
of its proper fluid : but this power ends in the organ 
itfelf. The organs of fenfe, the mucous furfaces at their 
origins, the nerves, &c. are fenfible to the impreflions of 
bodies which touch them, and moreover tranfmit thefe 
impreflions to the brain, which is the general centre of 
the fenfibilities of thefe various organs. 
Thus we have an organic and an animal fenfibility. On 
the former depend all the phenomena of digeltion, circu¬ 
lation, fecretion, exhalation, nutrition, &c. it is common 
to plants and animals; the zoophyte enjoys it as well as 
the molt perfectly organized quadruped. From the latter 
flow the fenfations, perception, and pleafure and pain, 
which modify them. The perfection of an animal is in 
proportion to the degree in which he enjoys this fenfibi¬ 
lity. It is not an attribute of vegetables. 
The difference in thefe two modifications of fentient 
power is well marked in the mode of their termination in 
fudden deaths. The animal fenfibility is immediately 
extinguifhed. There is no trace of this faculty left in 
the inltanf which fucceeds a powerful concuflion of the 
brain, a great hemorrhage, or an afphyxia: but the 
organic fenfibility ftill fubliits for a longer or fliorter time. 
The lymphatics ftill abforb; the mufcle quivers when 
pricked ; the nails and hairs even feem to grow. All 
traces of this fenfibility are not deftroyed until after an 
interval, occalionally of confiderable ftrength. 
Yet the efl'ential nature of thefe two powers is probably 
the fame. In many parts they are connected together 
and fucceed each other in an infenfible manner; as we 
may obferve in the origins of the mucous membranes. 
Weave fenfible of the paffage of the food through the 
mouth, and the pharynx: this fenfation becomes weaker 
in the beginning of the cefophagus, almoft ceales in the 
middle of that tube, and difappears at its lower extremity 
and in the ftomach, where the organic fenfibility alone 
remains. The urinary and generative organs exhibit 
exaClly the fame phenomenon ; there is animal fenfibility 
near the fkin ; it gradually diminifhes, and becomes at 
laft organic in the interior of the organs. 
Different ftimuli, applied to the fame organ, excite in 
it one or the other of tiiefe fenfibilities. When ligaments 
are cut, or irritated by acids or alkalies, they do not 
tranfmit to the brain the ftrong impreflions which they 
receive. But, if they are twilled, diftended, or torn, 
acute pain is the conlequence. The blood circulates in 
the arteries without our feeling it; but injeCt an extra¬ 
neous fluid, and the cries of the animal fliow that he is 
fenfible to the impreflion. 
We daily obferve inflammation, by increafing the or¬ 
ganic fenfibility of a part, transform it into animal fenfi¬ 
bility. Cartilages, ferous membranes, &c. which, in their 
ordinary ftate, have only the obfcure fenfibility necefl'ary 
for their nutrition, become endued, when inflamed, with 
animal fenfibility, often more acute than that of the 
organs in which it relides habitually. Inflammation ac¬ 
cumulates the vital properties in a part, and thereby 
changes the organic into animal fenfibility, which differs 
from it only in degree. 
The diftindtion now explained does not arife from the 
nature of the faculty, which is every where the fame ; 
but is founded on the different modifications of which it 
is fufceptible. The power is common to all organs, and 
forms their true vital character; but it is diftributed in 
different proportions, and bellows a different mode of 
exillence on each. In thefe varieties there is a certain 
meafure, below which the excited organ alone receives 
and perceives the fenfation; and above which it is trans¬ 
mitted to the brain. 
Vol.XX. No. 1372. 
Although each organ exhibits continual varieties in its 
fenfibility, yet it feems to pofl'efs originally a certain pro¬ 
portion, to which it always returns after thefe alternations 
of augmentation and diminution. This proportion con- 
ftitutes the proper‘life (vita propria) of each part, and 
fixes the nature of its relations to thofe bodies which are 
foreign to it, but which often come in contadl with it. 
The lalivary, pancreatic,and biliary, dudts,having a propor¬ 
tion of fenfibility exadtly analogous to the nature of the 
fluids which pafs through them, admit thofe readily, but 
rejedl all others. The larynx-refufes admifiion to every 
thing except the air. The excretory tubes are in contadl, 
on the mucous furfaces, with various fluids that pafs over 
thefe furfaces, but they never allow them admifiion. In 
the fame way the ladteals, which open on the furface of 
the inteftinal canal, abforb chyle only, and not the fluids 
which may be mixed with it. Thefe relations do not 
exill only between the different proportions of fenfibility 
in the organs, and the various animal fluids; they may 
alfo take place between external matter and the parts of 
the animal frame. The particular fenfibility of the blad¬ 
der and kidneys, and of the falivary glands, eftablifhes the 
relations between thefe organs and cantharides, mer¬ 
cury, See. 
It may be enquired, why nature, in the diftribution of 
the different proportions of fenfibility, has bellowed this 
property only in inferior degrees on the internal organs, 
or thofe of the interior life, while fhe has fo abundantly 
provided with it the external organs ? why, confequently, 
each organ concerned in digeltion, circulation,-refpiration, 
nutrition, abforption, does not tranfmit to the brain, the 
impreflions which it receives, while all the adls of the 
animal life fuppofe this tranfmiflion ? The reafon feems to 
be, that all the phenomena, which eftabliflt our relations 
to furrounding beings, mult be, and are in effect, under 
the influence of the will, while thofe, which are fubl'er- 
vient to the purpofes of afllmilation, ought to be exempt 
from that influence. To make a phenomenon dependent 
on the will, we mull be confcious of it : to exempt it 
from the influence of that power, this confcioufnefs mult 
not exilt. 
Of Contractility. — Contra£lion is the rnoft common 
form of motion in the animal organs. Some indeed move 
by dilatation, as the iris, corpus cavernofum, &c. but we 
know as yet fo little of this kind of motion, that we fliall 
confine our remarks entirely to the former. 
Spontaneous motion, a faculty inherent in living bodies, 
prelents, like fenfibility, two great modifications diftindt 
from each other, as we obferve it in the phenomena of the 
two lives: thefe are the animal and the organic contrac¬ 
tility. The former, fubjedl to the will, has its origin in 
the brain, ceafes to exill when the organs no longer com¬ 
municate with the brain, and participates in all the af¬ 
fections of that part. It refides exclufively in the volun¬ 
tary mufcles, and prefides over the functions of locomo¬ 
tion and the other movements, and the voice. The lat¬ 
ter, not dependent on any common centre, has its origin 
in the part, is not connected with any voluntary adts, and 
produces the phenomena of digeftion, circulation, fecre¬ 
tion, &c. Like the correfponding fenfibilities, they are 
efl'entialfy diftinguifhed in violent deaths, which fuddenly 
annihilate the animal contractility, allowing the organic 
ftill to exert itfelf for a longer or fliorter time. The fame 
difference is obferved in afphyxia, which fo much refem- 
bles death : the animal contractility is entirely fufpended, 
the organic ftill continuing adtive. In paralyfis, alfo, vo¬ 
luntary motion is deftroyed, while the organic movements 
ftill go on. 
Thefe two kinds of contradlility are connected to their 
correfponding fpecies of fenfibility. The fenfations pro¬ 
duced by external objedts bring the animal contradlility 
into exercile ; and, before the organic contraction of the 
heart takes place, its fenfibility has been excited by the 
contact of blood. Yet the connexion is not the fame in the 
two cafes. The animal fenfibility may be excited, with- 
4. S out 
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