ANATOM Y. 
53 ° 
to be peculiarly fitted, by poffeft'ng a degree of fenfibllity 
much inferior to that of the more important parts of the 
fyftem. Under all the modifications which we have now 
mentioned, cellular fubftance appears to have few blood- 
veffels., and no nerves ; at leaf! no nerves are vifible. But 
we muff conclude, that the few blood-vell'els w hich con- 
vey-nutrition to the cellular fubftance mu ft be accompa¬ 
nied with nerves, however minute. And the feeling which 
can, by difeafe, be awakened in thefe parts, mud lead us 
to infer, that they are in lome degree fupplied with nerves; 
as vve cannot conceive that fenfation can be produced, ex¬ 
cept by the .agency of nerve. The paucity, however, of 
blood-v.eliels and nerves in the cellular fubftance, fuffi- 
ciently evinces, that thefe parts can be little fufceptible of 
the aCtion of ftimuli; and the fact which vve thus difcover 
from the ftruCture of the parts, is ftrikingly evidenced by 
experiment. Under all its diff erent modifications, cellular 
fubftance in the healthy ftate appears to be infenfible to the 
aCtion both of mechanical and chemical ftimulants. The 
tendons of animals have been cut and pieiced, they have 
been pinched and torn, the actual cautery, as well as the 
chemical, have been applied, without inducing the leaft 
indication of pain in the animal fubjeCted to the experi¬ 
ment. The mod violent chemical ftimuli have been ap¬ 
plied to the various parts of a joint, without producing 
any appearance of an uneafy fenfation. In like manner, 
in chirurgical operations, the various modifications of the 
cellular f ubftance may be operated upon without producing 
any degree of pain to the patient. Nay, it appears that 
little pain is induced by the accidental laceration of the 
ligaments and tendons. We cannot indeed fay that thefe 
parts are entirely without feeling. Their feniibility is 
indeed dull. They receive the impreflions of ftimuli very 
flowly; but when, by difeafe, the orginization of the 
part is deranged, the feeling is aftonifhingly increafed, and 
the patient buffers a more acute pain than what we obferve 
in almoft any other part of the fyftem. One thing, how¬ 
ever, is obvious, the organ of fenfation in thefe parts mu ft 
be precifely the fame as in the reft of the body. It is only 
to the nerves that we can afcribe this quality. They may, 
in the cellular fubftance, during the ftate of health, be 
peculiarly fheathed and defended from impreflions to 
which they become expofed when the organization of the 
part is injured by difeafe. 
In the mufcular and nervous fibre, we perceive the 
powers of life exerted with much greater activity than in 
tliofe parts which vve have hitherto noticed; or, more 
properly fpeaking, mufcular and nervous fibre are much 
more fufceptible of the action of ftimuli, than bone, car¬ 
tilage, or cellular fubftance. It is by impreflions upon 
thefe, by the operation of various agents, that every power 
of the body is awakened and called into aCtion. The 
mufcular and nervous fyftems appear to be fo intimately 
connected, that fome phyfiologifts have imagined that 
mufcular fibre is a mere continuation of the nervous mat¬ 
ter. Anatomy inftantly refutes this opinion : the nerves 
enter into the mufcles in every poflible direction ; and we 
may trace their brandies and ramifications perfectly dif- 
tinct from the mufcular fibre. We cannot indeed trace 
their courfe to their termination, becaufe they become 
deprived of their external coats, mere medullary matter 
remains, and difappears among the mufcular fibres. It is 
perhaps ftill more clear, that mufcular fibre is not a con¬ 
tinuation of nerve, becaufe mufcles in the limbs of animals 
do not diminifh in magnitude, although the nerves enter¬ 
ing thefe mufcles have been cut through fora confiderable 
period. Yet there certainly exiftsan intimate and univerfal 
connection between the mufcular fibre and the nerves; 
becaufe neither the one nor the other can be added upon by 
any ftimulus, without the whole body being affeCted in a 
greater or fmaller degree, according to the nature of the 
part, and the powers of the ftimulus applied. We find 
then that both mufcular and nervous fibre are fufceptible 
cf impreflions from ftimuli; but it is alfo true, that the 
effects produced on thefe two fubftances in fome refpeCls 
vary. Thefe differences will appear from the fhort account 
which we fliall here give, beginning with mufcular fibre. 
Every diftintt mufcle is formed of a congeries of longi¬ 
tudinal fibres, which are connected together, as we have 
already hinted, by the cellular fubftance. They are ex¬ 
tended from bone to bone, and from part to part, fo.as to 
form an almoft univerfal covering to the bones, and are at 
the fame time the inftruments by which all the motions of 
the bones are performed. Each congeries of mufcular 
fibre appears difiinCt from the reft, being terminated at its 
origin and infertion by its proper tendons, which, as we 
have faid, are a modification of the cellular fubftance. 
Thofe.mufcles which are not inferted into any of the bones, 
as the fphinCters and mufcular membranes of the vifeera 
and veffels have commonly no tendons. Tliofe, aoain, 
the origin and infertion of which are on different bones 
and in the more moveable extremities, are generally fup¬ 
plied with long tendons, which pafs round the joints and 
heads of the bones to be inferted in the more moveable 
part. But, however difiinCt the different mufcles appear, 
there is an univerfal connexion, which depends upon the 
univerfal diftribution of the nerves; one or more of which 
enter into each mufcle, and thus form an indivifible whole. 
The mufcles are alfo abundantly fupplied with arteries 
and veins, which enter within the cellular coat that fur- 
rounds the mufcular fibres, and, running in company with 
each other, are fubdivided, and form a kind of reticular 
work. From the fmaller of thefe veffels a vapour and 
febaceous matter are fecreted into the cellular fubftance, 
and which are again abforbed by lymphatics, the prefence 
of which is alfo perfectly obvious, both on the furface 
and in the fubftance of the mufcles. The ultimate fibres 
of the mufcles appear to be final 1 foft threads : when fub- 
jeCted to the microfcope, they exhibit a kind of wave or 
zigzag appearance. This form has been attributed to the 
impreflions made by the veffels, cellular fubftance, and 
nerves, upon the fibre. Dr. Monro has however demon- 
ftrated a fimilar appearance in the tendons and nerves; 
and he is of opinion, that thefe undulations are a kind of 
folds or joints, which ferve to accommodate the parts to 
the different ftates of flexion and extenfion. In proof of 
this, he obferves, that thefe appearances are only prefent 
when the parts are in a relaxed ftate, and that they en¬ 
tirely lofe it when much flretched. 
Many opinions have been entertained with refpeCt to the 
ftruCture of the mufcular fibre: it has been fuppofed that 
they are folid ; again it is faid that they are hollow, beinw 
formed of a feriesof veffels or rhomboidal chains commu¬ 
nicating with each other ; and laftly, it has been alleged, 
that they are full of a kind of down or woolly fubftance. 
The faCt cannot be determined by the eye or the micro¬ 
fcope, and therefore we conceive it not worth while to 
engage in the difpute. Indeed, as far as we can difcover, 
the mufcular fibre, when wafiied from the blood contained 
in the veffels which accompany it, appears a white foft 
folid. Thefe delicate fibres, formed into bundles of dif¬ 
ferent magnitudes, and varioufly difpofed, fupplied with 
blood-veffels and abforbents, joined together, and fup- 
ported by cellular fubftance, and united together, fo as to 
form one grand fyftem, by the diftribution of nerves, are 
deftined to perform the mod important offices in the body. 
Every motion is produced by their operation. They pof- 
fefs a kind of contractile power, by which they are fitted 
to propel the blood from the heart, and direCt its courfe 
through all the numberlefs channels in which it flows 
throughout the body. They produce the aCtion of the 
lymphatics, by which abforption is carried on ; by their 
energy, every fecretion and excretion of the fyftem is per¬ 
formed ; the important function of refpiration depends 
upon their exertion ; and they effeCt the various motions 
of the body, which are of fo much utility in the different 
avocations of life. To render them capable of producing 
thefe effeCts, they are in a high degree endowed with that 
z fufeep- 
