HEA R°T. 
lated in the right cavities, and makes them appear the 
lareeft 
Thus we have arrived at two flatements, which ate gene- 
rally true: rft, that the great tree, which terminates the fyf- 
© fame ebfervations applies to the two fides of the heart, which 
~ The cafe,”’ fays Bichat, “is not the fame with the tree 
in which the fyftem of black blood ends, when compared with 
t in which the red-blooded fyftem commences. ‘I'he pul- 
r ry, and the veins of the fame name, prefent a lefs 
confiderable difproportion in their capacity than is obferved 
between the two kinds of veffels in other parts; yet there 
is a real difference, and that is in favour of the veins. Since 
the artery is continuous with the veins of the body in gene- 
pected that thefe canals fhould correfpond relatively to each 
other. The phenomenon may be explained by the difference 
in the velocity of the blood: that fluid circulates more ra- 
pidly in the pulmonary artery, than in the veins of the fame 
ough thefe veins. ence the two circumftances, 
ity of the blood’s motion, and the capacity of the 
other in the two oppofite trees, which form each vafcular fyf-. 
tem, In that of red blood there are diminifhed velocity and. 
greater capacity from the pulmonary capillaries to the agent 
of impulfion: from the latter to the general capillary fy{- 
tems, we obferve, on the contrary, increafed velocity and 
diminifhed capacity. In the other fyftem the charaGters firft 
mentionéd prevail from the general capillaries to the impel- P° 
ling power : and the other circumftances are feen in the fe- i 
m. 3 
cond part of the fyfte 
- The capacity of the pulmonary veins,. however, furpaffes 
that of aort i 
or 
pulmonary veins. The following reafons feem fufficient to 
_ explain this arrangement. As the courfe of the pulmonary 
veins is very fhort, the impulfe received yy the red blood 
— pulmonary capillaries is more effeétu 
many caufes of retardation, which affe& the 
pulmonary veins, — | 
- exerted, | 
3 ‘ Cave, are 
Hence greater velocity and lefs diameter: in the b 
and. why the coronary and ven cave are fo difproportionate 
to the pulmonary artery. ; og. 
If there were no impelling power in the tivo fyfle 
their capacity would be uniform throughout, beat Pras 
velocity would be the fame inall parts. Hence in the abdo. 
minal fyflem ef black blood, the hepatic and inte inal | % 
tions of the vena portarum are of equal capacit Pe é 
flow motion of the contained fluid, and confiderable capa- 
at 3 and wh 
the arteries are marked by three oppofite charaGters. en 
too we underftand, although the red and the black blood 
form in their whole courfe one continuous column, and 
nearly the fame in the whole extent of each fyftem, why the 
organs placed on the exterior of this membrane fhould be 
fame reafon, the diameter of the veins exceeds that of the 
arger branches, which, by their fubfequent junctions, com- 
e {maller venous tubes 
re lodged in the intervals o parts, as between the lobes’ 
than the 
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