probably is in the direction of the blood’s motion,
assisted by lateral pressure of all kinds; because
the valves will favour this course wherever they
are. However, as the valves are not universal,
the motion of the blood in some veins must be
carried on without them, and therefore they are
not absolutely necessary.
“ When treating of the motion of the blood,
in the arteries, I observed that its motion was not
an uniform stream, but interrupted, which arose
from the heart’s action ; but that as it receded
from that viscus, that its motion gradually became
more uniform, till at last it was nearly a continued
stream. However, it is not certain, but an alternate
accelerated motion is continued into the
veins, immediately from the heart, although it
may not be an easy undertaking to ascertain this f
for simply observing an accelerated motion
in the blood of the veins, more especially the
small ones, does not prove that this was an alternate
increase immediately from the arteries.”
H Even breathing produces a stagnation near
the thorax; for during inspiration the veins
1 This is readily done, as will be seen shortly, by observing the
circulation in the web of the frog. M. If.
readily empty themselves; but in expiration there
is a degree of stagnation. Coughing, sneezing,
or straining, in any way where the thoracic and
abdominal muscles are concerned, produces this
effect.” 1
After these names I must mention that of Hux-
ham, who, in a remarkable paragraph, has anticipated
Dr. Barry, as far as mere conjecture can
anticipate experimental proof:—
“ Thus much of the power of the air in the
lungs ; let us now briefly see what effect it hath on
the whole body.
“ First then, let us consider the air as a heavy
circumambient fluid perpetually pressing upon us ;
so that a man of a middle stature sustains from it
no less than a weight of 32,0001b. an immense
load which would press out every drop of juice
that is in us, unless the pressure was equal on all
sides, and the blood and humours in the vessels
equally resisted the pressure, so as to keep up a
kind of equilibrium. And this the most wise
Creator of all things hath made most highly useful
to us, for it not only conserves and strengthens
the whole frame of the body, but confines its
1 Treatise on the Blood, &c. Ed. 1794, pp. 185—187.