PHYSIOLOG Y. 
362 
which enters from without is firft received into this cir¬ 
culation. The chyle, or the produce of the digeftive 
functions, is conftantly conveyed into the general canal, 
and circulates there. The gafeous matters which tra- 
verfe the lungs in the aCt of refpiration, are mingled with 
the blood in the fame place. Laftly, whenever abforption 
takes place from the (kin or the mucous membranes, the 
black blood firft receives the product. Hence fhecircula- 
tion of black blood may be regarded as a general refervoir, 
receiving in the firft place all tliofe fubftances which are to 
be expelled from the body, and all which are tobe admit ted.’' 
We have now to mention the arguments with which 
the notion that the arteries dilate and contract have been 
oppofed. The reader will obferve, however, that the 
difcuflion of this fubjeCt has been very warmly entered 
into by us in the article Pathology. 
If the pulfe were produced by vital contraction of the 
arteries, it fiiould be irregular below an aneurifmal tu¬ 
mour, fince the difeafed condition of the arterial tiffue 
would naturally be expeCted to deftroy or confiderably 
modify this power. But no fuch effect is obferved; 
while, on the contrary, organic difeafes of the heart con¬ 
ftantly affeCt the pulfe. Oftification of an artery does 
mot obftruCt the blood’s paffage, but the change has the 
mechanical eft’eCt of preventing us from feeling the pulfe. 
A ligature placed on an artery, by intercepting the in¬ 
fluence of the heart, flops the pulfe in the vefl'els beyond 
the fituation of its application. That the phenomenon 
of the arterial pulfations is not owing to any contraction 
of the vefl’els is proved by the following curious experi¬ 
ments of Bichat. “ Take the arm of a dead fubjeCt, and 
place it in warm water; then infert a fmall tube in the 
brachial artery, and fix its other extremity in the carotid 
of a large living dog. Immediately the heart of the ani¬ 
mal will propel the blood into the dead limb. The ar¬ 
tery pulfates lefs ftrongly indeed than in the living ftate, 
but quite fufficiently to admit of the eft'eCt being felt even 
through the.integuments. When the red blood is made 
to circulate in the veins by a contrivance of this kind, 
there is ah effeCt produced fenfible to the finger, and the 
fluid moves with confiderable rapidity. The latter ex¬ 
periment alone is almoft fufficient to prove that the heart 
is the only agent by which the blood is made to move 
through the arterial tubes. In faff this fluid flows uni¬ 
formly through the veins, becaufe the capillary fyftem 
fupplies them uninterruptedly, while it is thrown out of 
an artery by fucceflive jets, which arife from the contrac¬ 
tions of the heart. Now, if you open a vein in which 
you have introduced red blood by means of a bent tube 
connected with the artery of another animal, the ftream 
of blood will exhibit the jets correfponding to the con¬ 
tractions of the heart. If this experiment be inverted, 
that is, if a bent tube be adapted to a vein and an artery 
in fuch a manner that the blood of the former may be in¬ 
troduced into the latter, the artery will lofe its pulfation, 
unlefs it ftiould be kept up by the collaterals, which will 
not be the cafe if large trunks, fuch as the crural and its 
correfponding vein, be feleCted. The refult of all thefe 
experiments, which I have frequently repeated, ought to 
have been exaCtly the converfe of their aCtual refult, if 
the arteries participated in the circulation by their vital 
powers. The aCtion of the heart will drive the blood 
through dead tubes of confiderable length adapted to the 
arteries. Remove a portion of the carotid, and infert a 
pipe into its open ends: the blood will traverfe this, and 
cccafion the arteries to pulfate beyond the fituation of 
the experiment. Infert the end of a tube in the carotid 
of a dog towards the heart, and itsoppofite extremity in 
the crural or carotid of anotherdog in the direction lead¬ 
ing from the heart: the heart of the firft will conftantly 
produce pulfation in the arteries of the fecond. If a 
tube, having a bag of fome kind at its end be inferted in 
an artery, the blood immediately fills the bag, in which 
there will be a kind of pulfation at each aCtion of the 
ill ear t, analogous to what is felt in an aneurifmal cyft.” 
As a further proof that the pulfe is produced by the 
heart’s aCtion, Bichat mentions that he expofed the ca¬ 
rotid artery and the heart by a feCtion of one fide of the 
cheft, in the fame animal; the other fide ftill remained 
for refpiration. The pulfe was at firft hurried, as the 
contadi of the air accelerated the contractions of the 
heart; but, in a little time the motions grew weaker, and 
were foon performed by a general quivering of the fibres. 
The pulfe underwent a correfponding change; when the 
convulfive motion took place, the beating of the artery 
was converted into a kind of undulation, or weakofcilla- 
tion, which is the precurfor of the total ceffktion of all 
motion. “ Nature,” fays the fame author, “ has feleCted, 
for the compofition of the arteries, a tiffue in which the 
vital properties are indiftinCtly marked. In proportion 
as thofe of the heart are remarkable for their intenfity, 
are the arteries confpicuous for the oppofite reafon. In 
this refpeCt they mult be clafled with the cartilaginous, 
fibrous, fibro-cartilaginous, and fimilar fyftems. Nature 
feems to have organized the arteries in this manner, that 
their motions might not difturb the unity of the impulfe 
produced by the heart. Suppofe their vital powers had 
refembled thofe of the inteltinesj a convulfive aCtion of 
the aorta or the large trunks might have flopped the cir¬ 
culation, and produced the moll alarming effeCts by coun¬ 
teracting the exertions of the heart. The more atten¬ 
tively things are examined, the more perfectly fhall we 
be convinced of the necefiity that there fiiould be only a 
Angle impelling agent for the arterial fyftem, and that the 
latter, conftantly inert, ftiould not have the power of ar- 
refting the motions of the contained fluid.” 
The aCtion of the heart on the red blood ceafes, accor¬ 
ding to Bichat, in the general capillary fyftem, where the 
place of its influence is fupplied by the tonic powers of 
the fmall vefl'els. “ In the trunks, the branches, and the 
fucceeding divifions, (according to the opinion of this 
phyfiologilt,) the blood is moved only by the heart; in 
the fmall ramifications the vital aCtion of the arteries 
concurs with this force in keeping up the blood’s mo¬ 
tion ; and, laftly, in the general capillary fyftem the vi¬ 
tal aCtion of the vefl’els is the only power employed. 
The pulfe, therefore, is only obferved in its greateft ex¬ 
tent in the firft orderof tubes; it isfenfibly weakened in 
the fecond; and entirely ceafes in the capillary fyftem. 
In the large trunks, the impulfe produced by the con¬ 
traction of the heart is fo ftrong, and the column of 
blood fo large, that the infenfible contraCtility has no 
eft'eCt. Irritability alone might a Cl in this fituation, but 
that property does not exilt in the veflels. In the fmall 
tubes the eft'eCt of the heart’s aCtion is fenfibiy diminifhed ; 
and the blood, divided into very (lender (treams, requires, 
for the maintenance of its motion, merely a kind of ol- 
cillation, or infenfible vibration of the valcular parietes. 
This companion fhows us the eflential diftinCtion of the 
two kinds of organic contraCtility. The one is exerted 
on the fluids when accumulated in a mafs, as on the 
blood, aliment, urine, &c. the other moves them when 
divided into (mailer portions, and prefides over the capil¬ 
lary circulation, exhalation, and (ecretion. Wherever 
there is a large cavity, as in the heart, ftomach, inteftines. 
See. the former is efpecially obferved, while the fecond is 
confined to the cafe of fmall vefl'els. Hence, while the 
blood continues in maffes, as in the heart and large arte¬ 
ries, the firft of thefe powers, which reftdes in the heart, 
produces its motion ; when it is in (mall (treams, the in¬ 
fenfible contractility of the vefl'els keeps up the movement.” 
Phenomena produced by the Action of the Heart .—As the 
arteries are always full of blood, the impulfe produced by 
the contraction of the left ventricle is felt at once through 
the whole fyftem to its very extremities. If a tube, di¬ 
viding into a feries of branches, which were again divi¬ 
ded for any number of fucceflive times, and completely 
filled with fluid, were connected to a fyringe, the de- 
preffion of "the p.ifton would caufe an efflux from all the 
open branches at that very inftant. In the fame way, if 
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