345 
PHYSIOLOGY. 
agencies, but we think without caufe. The firft is noted 
by its keeping the refpeftive particles of the mufcle con- 
ftantly in a certain degree of approximation. This is not 
the mere cohefion of inanimate matter. With the cef- 
iation of life in general, this alfo ceafes, though flowly ; 
and the degree of its force is always in proportion to the 
force of the other law of contra&ility, prelently to be 
noticed. The agency of this (as we may perhaps term it) 
conjiant contraction is greater in fome perfons than others, 
in lome animals than others, and we believe is always 
ftrongeft in the healthieft animals. Indeed firmnefs of 
flelh is always held to be a criterion of ftrength. This 
kind of contraction may be much increafed by ftimulus, 
as well as the more fudden contractions. This faft w'e 
obferve in the fixed rigidity of limbs induced by difloca- 
tions. This power is much influenced by the nervous 
fyftem; hence the well-known practice in the accounts 
mentioned of debilitating the nervous fyftem, before we 
attempt to conquer by force the refiftance of the mufcles. 
Whatever weakens the fudden contractility alfo debili¬ 
tates this power. It has been commonly named tone, or 
tonicity; and it always operates, as we before faid, on 
animal matter for fome time after death; and, even when 
loft, its effeCt (viz. the approximation of the mufcle to a 
fpecific extent) remains till extenfion be applied. Thus, 
in dead bodies, mufcles retain their peculiar Ihortenings 
until, by much handling on difieCtion, they are length¬ 
ened as far as the mechanical ftruCture of their formation 
will allow. 
The next modification of contractility is that by which 
the limbs are moved. The natural ftimulus of the 
mufcle to produce this effeCt is, as we before obferved, 
nervous influence. As a general rule, it may be ftated, 
that the energy of mufcular contractions accords with 
the fize of the mufcle in which this act is exhibited. 
Contractility of this fudden kind differs from the one juft 
mentioned, in that it becomes feebler in proportion to 
its exercife, but acquiring ftrength by reft. In the more 
perfeCt animals, it is, like other functions,much dependent 
on nervous and vafcular influence; and a certain propor¬ 
tion of oxygen and heat is effential to its exiftence. 
The nature of thefe influences, and their degree, are not 
however certain. 
Though we have found fome difficulty in explaining 
what ftruCtures contractility inhabits, we may affert, that 
in man and in the more perfeCt animals it is confined to 
that portion of the frame called mufcle (the lean of meat), 
and to the blood; and that there is no comraCfility 
whatfoeverin the cellular membrane, except fuel) as is a 
fecondary effeCt of the fullnefs oremptinefs of the veffels 
which contribute to form that ftruCture. It is proper, 
left we be confidered to have difmiffed the fuhjeCt of the 
ultimate mufcular fibre too abruptly, to mention the 
chief ipeculations on this head. We borrow the analy- 
fis from a contemporary. Much contrariety of evidence 
exifts as to the intimate ftruCture of mufcular fibres. 
Leeuwenhoek reprefents them as being exceedingly mi¬ 
nute, many thoufand uniting to form one vifible fibre ; 
but that they differ confiderably in diameter in different 
animals, without any relation to the fize of the animal. 
He ftates, for example, the fibre of the frog to be larger 
than that of the ox. He thinks their fize alfo varies ac¬ 
cording to the age of the animal, being fmalleft in the 
earlier periods of life. Muys, who was engaged for many 
years in the moft laborious researches on this fubjedt, con¬ 
cludes, on the other hand, that the real ultimate fila¬ 
ments of mufcles are in all cafes of the fame fize, even 
when compared among the mammalia, birds, and infeCts. 
Prochalka, again, fays exprefsly, that they are not all of 
the fame diameter, but differ in different animals, and 
even in different parts of the fame animal. Their dia¬ 
meter has in general been ftated as lefs than that of the 
globules of the blood; but Sprengel fpeaks of them as 
being equal to the 500th of an inch in the mammalia, 
and the 250th in birds and fillies. Some microfcopical 
Vol. XX. No. 1373. 
obfervers have reprefented them as hollow' tubes; but 
this is probably an optical deception, like that which has 
led to the belief that hairs are tubular. Several, fuch as 
King and Tauvry, have imagined them to be continua¬ 
tions of arteries; an opinion which was conneCled with 
the theory of the indefinite extenfion of vafcularity, 
formerly prevalent, but fince fufticiently refuted by ob- 
fervation as well as reafoning. Prochafka afferts, with 
confidence, that they are folid, and of a polyhedral prif- 
matic lhape, generally flattened, or thicker on one fide than 
on another, fo that a tranfverle fedlion prefented an ap¬ 
pearance fimilar to that of bafaltic pillars. Hook and 
Swammerdam reported the fibres to be compofed of a 
leries of globules; Cooper and Stuart fuppofed them to 
be cellular; and Borelli that they were formed of a ftring 
of rhomboidal veficles. Fontana’s account of them in 
general agrees with that of Prochaika; but he remarks, 
that they are furniftied, at regular intervals, with tratif- 
verfe bands; and that they may always be diftinguilhed 
by their parallel difpofition from the fibres of membrane, 
which are more or lefs contorted. Sir Anthony Carlifle 
ftates, that a mufcular fibre, duly prepared by wafliing 
away the adhering extraneous fubftances, and expofed to 
view in a powerful microfcope, appears to be a folid 
cylinder, the covering of which is reticular membrane, 
and the contained part a dry pulpy fubftance, irre¬ 
gularly granulated, and of little cohefive power when 
dead. Mr. Bauer reprefents them as compofed of a 
row’ of globules, exadlly correfponding in fize to thofe of 
the blood, when deprived of their colouring matter. By 
long maceration in water, the cohefion of thefe globules 
is loofened, and the fibre is broken down into a mafs of 
globules. 
Before difmifling mufcular contradtion, it is requifite to 
account for the power which elongates this ftrudture after 
its retradfion. This is Amply mechanical elafticity, a 
property perfedtly fimilar to that manifefted in greater or 
lefs degrees by all bodies. This properly belongs to-that 
baj'al or fundamental ftrudture which has received fo many 
names; viz. cellular membrane, tunica cellulola, mucous 
tela, cellular lubftance, mucous tiffue, See. Whatever 
may be the name of this ftrudture, it holds together all 
parts of the body, whether mufcle, nerve, or bone. Con- 
denfed into membranes, it forms periofteum, peritoneum, 
ligament, cartilage, fynovial membrane, veffels, the 
covering of nerves, See. Of courfe, in all thefe cafes, it 
acquires a variety of alterations and of additions in regard 
to its ftrudture. One condition alone always accompa¬ 
nies it; it has abundance of minute veffels. On this does 
its freedom from decay depend. It has nerves alfo in 
various proportions. It is not always cellular; fo it is 
wrongly named. Its elafticity is ufed as a re-adting 
power, in many parts of the body, with excellent effedt. 
Like the mufcles, it has been often fubmitted to ultimate 
analyfis. It has been difputed whether this fubftance was 
refolvable into plates or fibres. Fontana had viewed it 
as an affemblage of cylindric fibres, which" w'ere twilled 
and interlaced with each other; but Monro has Ihown 
that he was deceived by an optical iilufion, to which the 
incautious ufe of the microfcope frequently gives rife. 
Bichat deferibes its intimate ftrudture as compofed both 
of filaments and of laminae, varioufly intermixed; and 
hazards a conjedture that the former are exhalent and 
abforbent veffels. Bordeu appears to have been the firft 
who advanced the opinion of the homogeneous nature of 
the cellular tiffue, which he compares to froth or glue. 
Quefnay confidered it more as a fluid than as an organized 
folid. Wolff rejedts entirely the idea of its being cellular, 
and regards it as a homogeneous and glutinous lubftance, 
without organization. Blumenbach, Platner, and Meckel, 
have adopted thefe views 5 after all, thefe various opinions 
feem worth nothing. 
The next elementary part in the body is the nerve. 
Till very lately it has been concluded by all phyfiologilts, 
that a nerve performs two functions; viz. one of tranf- 
, 4. T mitting 
