PATHOLOGY. 
192 
diftinguiflied authors have adduced the faCtof general inor¬ 
dinate habits of eating as an explanation of the frequency 
of plethora; but as, from the fails we have noticed under 
Dyfpepfm it is clear that gluttony mud lead for the moll 
part to indigeftion, and that to deficient nutrition we 
fhould be tempted to look for the caufe of this Hate. In 
the general diminution of fecretion, and in fail in fevers 
where this diminution is very apparent, a full Hate of 
the blood-veli'els is the moft formidable fymptom, and 
one which the moll copious abftraCtion of blood in many 
cafes fcarcely abates. 
The plethoric Hate may (though it rarely does) exilt 
in the fame degree in the fanguineous fyftem generally ; 
or it may be exceffive in all parts, but much more fo in 
one or more peculiar ftruCtures ; or, which is more com¬ 
mon, it may be exceflive in one part, and deficient in the 
reft. Under each of thefe circumllances, the blood-vef- 
fels are dillurbed in their functions; which brings us 
to the confideration of thefe latter parts. 
At page 28, we have detailed briefly the agents of the 
circulation, and have not hefitated to mention the con¬ 
tractility of arteries as one of them. In doing this, 
however, we were perfectly aware, that we were oppofed 
by the opinions and experiments of fome of our bell 
pathologills ; yet, on the other handymen of equal ta¬ 
lent, and the authors of experiments apparently con¬ 
ducted with equal precifion, fcrongly corroborate our 
view of the queltion. For our own parts, we pay little 
deference to thefe experiments which, from their very 
nature, can never be conclulive. Whoever will take the 
trouble to read over with attention the numerous hifto- 
ries of experiments detailed by Dr. Haltings, the lad au¬ 
thor who has performed experiments on this fubjeCl, will 
concur with us in this opinion. They will find, that in 
fome experiments the dilatation and contraction was not 
manifeft at all; in others, not for fome time; and in 
others immediately and unequivocally. Indeed we 
fhould naturally expeCt that thefe circumllances would 
occur to parts llimulated by unnatural means; and de¬ 
prived no doubt of much of the fluid of the vafa vacofum 
by the difleCtion necefl'ary for their expolure. 
We think, however, that this matter may be more fa- 
tisfaCtorily fettled by analogical reafoning than by the 
evidence of the fenfes, when that evidence produces 
fuch various appearances. By thofe who fuppofe that 
arteries aid the motion of the blood, it has been afierted, 
that the heart cannot propel that fluid through the round 
of the circulation ; but this afl'ertion has neither been 
proved nor difproved. One party fays that the heart has 
this power, for this reafon ; it is not required to drive 
the blood through the whole of the arterial and venous 
fyftems, fince an impreflion on the aorta by means of 
the left ventricle (the column ofblood being continuous) 
mult immediately, and without the hindrance of friction, 
be tranfmitted to that portion which the venous fyltem 
is pouring into the oppolite fide of the heart. But it is 
certain that this continuous column is liable to much 
variation; and hence it would feem more probable that 
the arteries lent fome aflillance to the heart. That the 
arteries have this power in fome animals is demonllrated, 
becaufe they have no heart; and, though Dr. Parry may 
fay, that “ if the circulation is carried on by any central 
force of whatever defcription, the apparatus in which 
that force refides is to all intents and purpofes a heart 
he mull in this cafe lhow how the ftruCture in queltion 
differs from arteries in common ; and that it does differ, 
the refearches of the accurate Sir Everard Home feein 
to deny. It might appear, that the dependence fome 
arteries have on the nervous fyftem, and that exclufively 
of the heart, was a ftrong argument in favour of the con¬ 
tractility of thefe veflels; but thofe who difcredit the 
exiltence of this property aflert, that this independent 
aCtion of the artery arifes from the debility of its pa- 
rietes, which gives way to the impulfe of the heart, and 
admits a greater flow of blood; this debility exprefling, 
according to them, a lofs of tonicity, or that degree of 
contraction which an artery is at all times exerting on 
its contents. 
W T e cannot help thinking that the truth of this refo- 
lutely-contefted point lies between. For, upon examin¬ 
ing the probable aCtion of tonicity, little difference will 
be feen between it and the phenomena of contractility. 
We mult remark, that tonicity is uled by one party to 
denominate a perpetual tendency to diminilh the calibre 
of the artery: contractility is ufed by the other left to 
defignate alternate contractions followed by aClive di¬ 
latation. ACtive dilatation is by no means probable, 
fince it is unlike the phenomena we obferve in other con¬ 
tractile ItruCtures of the body; fo that this mult be con- 
fidered the refult of the heart’s aCtion. But, with regard 
to the tonicity which Parry and others allow to arteries, 
they lay, that this is not the “ contraCtilite par defaut 
d’extenfion” of Bichat, but a vital power. If fo, is it 
too much to aflert that a vital contraCtile (truCture, which 
is expanded, will recover a fmaller calibre than it had 
originally ? To exemplify this, we fuppofe the fize of an 
artery equal to 3, and that the impulle of blood injeCted 
into it ltretches it to 4.. It may be inferred from the 
known power of contracting fibres in other parts of the 
body, that, the prelfure being removed, it will reduce its 
circumference to (fay) 2^ : and this overcomes another 
objection that has been made to fuppofing the contrac¬ 
tion and dilatation of arteries ; viz. that this dilatation 
might impede as much as accelerate the progrefs of the 
blood, fince it might exilt over the whole arterial fyftem 
juft at the time the left ventricle contracted. But, if 
the contraction be brought about in the manner we have 
Hated, it mult of courfe obferve the lame time in its con¬ 
traction as the heart itfelf, and confequently may mate¬ 
rially aflilt the circulation. 
We fhall alfume, therefore, in our (peculations on the 
Haematics, the contractility of arteries, ufing this term 
with the reftriCtion before Hated. We have before faid, 
that at the extreme branches of the arteries a motion is 
derived from a capillary attraction exilting between thefe 
veflels and the blood. This of courfe is no explanation, 
becaufe we do not know any thing about capillary at¬ 
traction. It may be ufed, however, to denote that the 
firme law governs the motions of the blood in thefe 
living tubes (to a degree) as in inanimate veflels. A 
motive power is again to be found in the fecernent fyl¬ 
tem : and here the data of reafoning become fewer than 
thofe on which it is founded, even with regard to the 
capillary arteries ; and we can only conjecture, plaufibly, 
that an attraction exifts between certain parts only of 
the blood and the Tides of the veflels ; and that the ad¬ 
dition of a fomething from the nerves is necefl’ary to 
change thefe parts of elements to the form they exhibit 
on fecreting furfaces, or outlets. Thepaflage of fluids 
in the larger abforbents, and in veins, we have before no¬ 
ticed. It was necefl'ary to recapitulate thefe circumftan- 
ces, that the whole of them might be borne in mind 
while treating of the difeafes of this fyftem. 
With regard to difeafes from quantity of blood, it is 
to be noticed, that an increafe in the mafs of blood fel- 
dom exifts unaccompanied by an increafe of the aCtion 
of the heart; when this does occur, the blood, although 
its quantity is increafed, will have its rate of motion di- 
miniflied. In fuch a cafe, the fmaller arteries, in which, 
as before ftated, the contractility is greater, in proportion 
to the fize of the veflel, than it is in the larger arteries, 
will, from the want of dilatation by means of the heart’s 
contraction, leflen their fphere of contraction, fo that an 
increafed proportion of the general mafs of blood will 
be contained in the larger arterial trunks, in the veins, 
and in the cavities of the heart. The whole round of 
the circulation will be obftruCted. The aCtion of the 
heart will confift of flow feeble contractions, or of inef¬ 
fectual flutterings. The pulmonic procefs will be imper¬ 
fectly performed: hence refpiration will be laborious and 
hurried. 
4 
