344 
PHYSIOLOGY. 
would unite fome of our divifions of elementary tiflues; 
this, however, only ffiows, that, in the abfence of fuller 
information, we have adopted the proper mode of fludy- 
ing the fubjedl, as will be clearly feen in the courfe of our 
progrefs. 
The firfl: agent obfervable in living forms is a tube 
capable of fusion. In inanimate matter, the fame agent 
is very generally met with ; but in vegetables and ani¬ 
mals it exills without an exception; and not only exifts, 
but almoft entirely com poles their flrudlures. The caufe 
of capillary attraction, or that power which produces the 
motion of fluids through tubes of fmall diameter, is 
unknown ; but the fadl is fufficiently certain. This phe¬ 
nomenon can be produced only thus : by an attraction 
between the Tides of the tube and the contained fluid, 
Itronger than the mutual cohefion which belongs to the 
particles of the fluid itfelf. The caufe of this attradfion, 
like the caufe of attradlions in general, we do not know', 
nor do we enquire, but fet out with the fadt as an ac¬ 
knowledged datum. This abforbing faculty, which ail 
porous bodies poflefs, is enjoyed by every plant; but 
with this additional and furprifing power, that not only 
does the vegetable tube imbibe the moifture or the air 
with which it comes in contadt, but it alfo decompofes 
and re-unites thofe fluids, and produces from them roots, 
flems, leaves, variegated bloffoms, and lufcious fruit. 
The great diverfity of the produdts would in this cafe lead 
us to infer a variety of different agents; yet certain it is, 
that minute veflels are the only parts in which thefe fur- 
prifing changes are effedled. How this happens, we per¬ 
haps lhall never know. If we cannot form the remoteft 
guefs at the caufe of that Ample attradtion before fpoken 
of, how lhall we learn thecaufes of this wonderful num¬ 
ber of attractions, fo diverfified in their effedls, and at¬ 
tached to fuch minute particles of matter ? We are com¬ 
pelled, therefore, again to take as a premife, that the ve¬ 
getable tube has powers capable of altering thecompofition 
of all the bodies it imbibes. It is probable, that, when 
knowledge is advanced, thefe powers may not be found 
fo various as they at firft appear. Great as the difference 
to common obfervers appears between the (tern and fruit 
of the tree, we may one day difcover that the operation of 
a very few tubes, pofiefled of different fpecies of attrac¬ 
tion, may be Sufficient to transfer the one into the other. 
This view of the fubjecl umuld indeed feem very clear, 
could we look at the plant or animal formed and adtive. 
We might fay, the veflels of this Item have affinities for 
one element of the fluids they come in contact with; we 
might fay, that the veflels of this flower has affinities for 
another; that the former part induces this change, and 
the latter a different one. But how thefe properties are 
acquired is molt furpriling, and cannot even be guefled at. 
How the little acorn fucks moilture from the earth may 
be conjedtured; but by what means every part of the 
future growth acquires the power of transforming the 
nutritive juices which are brought to it into its own pe¬ 
culiar form and nature, is not to be conceived. Confef- 
flng, then, that we cannot tell how this power is acquired, 
we afk how, being acquired, it adls. Much may be done 
(fpecific attradlions being granted to feparate vefifels) by 
mechanical arrangement. It is eafy to conceive, that, 
if water pafies along a veffel into which minuter veflels, 
having affinity for one component of water, open, this 
fluid, when arrived at its deffination, may have its nature 
perfedtly changed. 
Not to fpeculate longer on this fubjedl, we come to 
confider the fame power in animals. The zoophyte 
draws its nourifhment from the matter which furrounds 
it by the fame powers as the vegetable does. The more 
complicated animals differ from plants only in this; that, 
previous to the adtion of thefe abforbing tubes being put 
in force, the matter to be a b for bed has to undergo the 
diffolving procefs of a ftomach, or internal receptacle. 
This latter may alfo be confidered as a tube, in which, by 
the operation of final ler and varioufly-conftitu ted veflels,the 
firft part of aflimilation is accomplifhed. Now the effedl 
of the capillary tube ftill alluded to, is in animals more, 
furprifing than even in vegetables ; for the various parts 
of the former clafs are much more diverfified than thofe 
of the latter. The difcrepancies between bone, nerve, 
hair, and mufcle, are greater than exilt between flowers 
and fruits. Yet the reafoning which applies to the one, 
applies alfo to the other: all the fecretions of the body 
are performed in thefe fmall tubes; and though, on ac¬ 
count of their greater effedls, it feems neceffary that 
thefe powers fhould be fupported, and perhaps aided, by a 
diftindt power, (the nervous,) which we fhall prefently 
notice, yet we are warranted, from the fimilarity of eftedt, 
to infer that, in animals, as in plants, it is by thefe 
veflels that every compound ftrudhire is formed, every 
foreign matter abforbed, changed, aflimilated, or expelled. 
There is, however, another view of the fubjedl; but this 
cannot be noticed till we have defcribed the remaining 
elementary flrudlures. 
The next agent we have to notice is that which accom- 
plifhes motion. A power of moving is feen in animals and 
fome vegetables, no lefs furprifing than that of affimila- 
ting. Though attached to many and various apparatus, 
this power confifts Amply of a (hortening or retradlion of 
a peculiar ftrudhire, followed by elongation. This fliort- 
ening differs from that induced by the violent agencies 
of fire or eledlricify on inanimate matter in this refpedt: 
it is not accompanied by an apparent lofs or addition of 
fubffance: depending, like the phenomena of nutrition, 
on ultimate properties of cohefion, we cannot of courfe 
enquire how this contradhon is produced. It certainly 
requires peculiar arrangement or flrudlure, and the 
adtion of a fecondary agent. Plants poflefs it in a minute 
degree, but they do not feem to have a particular ftrudhire 
folely for the purpofe. The contradlions exhibited by 
fome plants, as the Mimofa pudica, and the Dionsea mul- 
cipula, or Venus’s fly-trap, (fo named from its curious 
adtion of crufhing any infedt which alights on its thorny 
leaves,) appear to be referrible to a very different fource 
from that of mufcular contradlility. 
In the prefent ftate of knowledge, it feems prudent to 
confider contradlility as a power inherent in mufcular 
fibres, without feeking to know what the ultimate Itruc- 
ture of thefe fibres may be, or whether this power, in- 
ftead of a Ample, may not be a compound eftedt. Many 
perfons have conceived that the nerves were the fources 
of contradlility ; but this does not feem to be the cale, 
becaufe, i.Contradlility can be excited by otheragents than 
nerves long after the latter parts have cealed to manifeft 
any life; 2. Though contradlions may be induced by 
galvanic influence applied to the remoter ends of mufcu¬ 
lar nerves, yet thefe contradlions are not more powerful 
than thofe produced by the application of the fame Iti- 
mulus immediately to the mufcular fibres; 3. Perfons of 
great nervous excitability are not more remarkable for 
the excefs in the contradlile power; Laftly, it is not pol- 
fible that contradlility can be entirely a nervous power ; 
the utmoll that can be faid is, that it is the compound 
effedl of nervous influence of matter of the particular 
form called mufcle. This laft view ot courfe very clofely 
approximates all differences of opinion on this head. 
The contradlility of mufcles appears therefore to us, as 
to Haller, a vis infita , a power independent of, and only 
called into adlion by, the nerve. 
There is fome difficulty in defcribing the ftrudlure to 
which contradlility is attached. Though in men and 
many animals it is found only in the red fibres, yet red- 
nefs is by no means indifpenfable to its exiltence, fince 
fifties, and other clafles that have this property in a very 
marked degree, have pale fteffi. Its local habitation is, 
however, we believe, always a fibrous arrrangement ; and 
in its chemical qualities refembles, or is identified with, 
that portion of the blood called fibrine. 
In the mufcular fyftem, contradlility prefents two phe¬ 
nomena which have befen referred by Bichat to feparate 
agencies, 
( 
