HEART. 
tiiflaken for the effect of irritability. This phenomenon is 
produced merely by the reflux of the blood, which not being 
able to pafs through the lungs, is accumulated in the pul- 
monary artery and right fide of the heart ; hence, when the 
latter contracts, as it finds an obftacle to the propulfion of 
its contents in the ordinary courfe, the blood is urged back 
again. This reflux takes place to a certain diftance, in fpite of 
the valves ; and is very perceptible, on many occafions, in the 
jugular veins, when animals fubmitted to experiments refpire 
laborioufly. It is alfo feenin the lait moments of life, when 
the pulmonary circulation begins to be troubled. The caufe 
of dilatation ceafing, the contractility of the veins reduces 
the veffel to its former ftate. 
This reflux of the black blood takes place, ina flight: 
, in the natural actions of the parts s the openings 
he veins free, the contraction of the auricle mu 
repel the contained fluid to a certain extent. 
Infenfible contra@ility, and its infeparable concomitant, or- 
ganic fenfibility, exiits in the veins as in other parts of the 
body, and is concerned merely with the bufinefs of nutri- 
i It is more ftrongly marked than in the arteries; at 
ey, a 
ihe) 
2) 
are mo 
The latter veffels 
ri and. their 
in confequence of injuries, 
exilt, The conditions neceflary to its p 
ganization of the veffel, as elafticity and refiftance, do not 
c ates of the circulation ; 
or the undulation caufed by making arterial blood circulate 
in them in experiments ; and in both thefe cafes the effe@ is 
Produced by the heart. 
“The blood moves through the veins in the following man- 
ner, pi 
conftantly pouring into the veins a certain quantity of blood. 
A general movement is communicated by this newly arrived 
portion to the former contents of the veffels ; and the addition 
atone end, as the fyftem is always i 
that fome fhould éfcape at the ‘other, or elfe the, venous 
Parietes would be dilated. Now, as thefe poffefs fome 
power of refiftarice, the blood flows on to the heart 
« However, the impulfe produced by the ister con- | 
traction of the’capillary fy itt weak to extend in- 
bse arteries, they would neceffarily tranfmit a portion o 
in, although they thould poflefs no valves. 
Cxceed the refiltance which it meets with, a very 
will difturb its motion, Hi ccalitty BF 
motion. : Inde a: 
Ht. "The aGtion of mutcles ; 
by the 
acceleration of thie jet im phlebotomy, 
The capillary fyftem, by its infenfible contraction, is’ i 
ins a 1 
_contftant uniformity of motion’tt 
full, renders it neceffary th 
to the heart, whenever a new quantity enters the -) 
the mufcles are exerted. In confirmation of this fatement 
we may adduce the abfence of varices from the deepfeated, 
and their frequency in the cutaneous veins. 2dly. The pul- 
fation of arteries has been fuppofed to accelerate the blood’s 
motion in the conti 
employment of bandages in ulcers and varices of the legs, 
isthe 
parts. 
“‘In general, the motion of the blood in the veins requires: 
many refearches for its elucidation ; the fubje@ is involved. 
in an obfeurity through which we can fciarébly difcern a few 
rays of light. The caufe of this is, that we do not know 
the kind and degree of motion communicated to’the blood in. 
the capillary fyltem, the influence of the vafcular parietes,, 
ir knowledge confilts merely of a few feparate views, 
tending more particularly to fhew the contraft between the 
circulation in the veins and in the arteries. A parallel of 
aogier . 
1 i 1at of the VEINS,. 
arieties in. 
@ movement in part of the venous fyftem; 2dly,. 
general famenefs in the degree of dilatation or contraétion 
uv all the arteries of the dead fabject; great variety in the 
veins of different parts. ere 
“To illuftratethe different motions of the arterial and venous. 
blood, fome authors have infifted much on this point’: that 
inthe arteries the blood is urged through tubes conftantly 
‘decreafing to the capillary fyitem, which relifts ; while in 
‘the veins it flowsin canals, always incréafing to the righ 
ricle, which offers no refiftance. But the black blood ofthe 
abdonien moves through decréafing tubés to. the capillaries of 
t@motion feems exactly fimilar to that in the 
°C 
the li 
iver,’ ari 
general veins. 
