Clarksville weekly chronicle. (Clarksville, Tenn.) 1873-1890, 1879-11-29
PSYCHOLOGICAL
AND COMMERCIAL.


Ieing an old Professor of Physi-
", we had better warn our
Hers that we are apt to expatiate
Susely when we get on the sub
of veins, arteries ard capilla-
]. We will, however, try to
hember that we are using some |
Is in physiology, not before a
s. Of medical students, but before
radiRg community interested in
interchange Of produce, for the
rtherance of which lines of travel
d traffic need to be opened and
pit up, so that when we speak of
different classes of blOOd-vessels
subservient to nutrition, secre-
IN and respiration, we do so with
lads and rivers and railways in
lr minds for the interchange of
Ericultural produce, raw material
Id manufactured goods. In short,
e are speaking in parallels, follow
g the example of Menenius
grippa when he pacified the pie
eians some three thousand years
go by his fable of the belly and the
hembers.
From the days of Harvey: the
siscoverer of the circulation of the
lood, down to some fifty years ago
ne functions of the heart, arteries,
capillaries and veins have been de-
cribed as follows: The ventricles
f the heart contracting on the blood
obtained in it force it outwards in
N directions through vessels called
lrteries; these branch off continu-
lily, becoming finer and finer, till
hey arrive at a system of vessels Of
microscopic fineness called capilla-
les, which form minute network
lervading every part of the body,
rom which it is taken up by the
finest branches of another system OF
vessels called the veins, and, pass
rng through them to larger and still
larger veins, is at last received into
the auricles of the heart, from
which it passes to the ventricles to
commence the course anew. So far
the description of the great discov-
.erer Harvey IL still accepted, but
his theory as to the forces which
keep this circulation always active
is no longer received. His idea was
that the heart did it all. He thought
that the forcible muscular contrac-
tions of the heart forced the blood
Through the arteries as through the
hose of a fire-engine, but continued
to propel it through the capillaries
and thence backwards to the auri-
cles of the heart, being aided in that
part of its course by sort of suction
power exerted by the expansion OF
the auricles. This theory is now
abandoned and the theory of capil-
larry force has been adopted. We
can't give the proofs for want OF
space, but it has long been demon
strated that the contraction of the
ventricles has no power to send the
blood further than the last ana
finest subdivisions of the arteries (;
that after this the blood passes
through capillary network by a
force something similar to that OF
chemical affinity. The blood is not
in exactly the same chemical con-
dition in any two points of its cir
culation. Thus before circulating
in the capillaries of the liver it
abounds in those chemical princi-
piles which constitute bile, and on
leaving that organ it is relieved Of
those principles; before entering the
capillaries of the lungs it abOunds
in carbon and is defective in OXy-
gen, while after circulating there it
has exchanged carbon for oxygen.
Again, on entering the capillaries
of a muscle it is rich in the material
for building up the muscular sub
stance, and, on leaving it, it has
deposited that material and is
loaded with the refuse substances
resulting from the decomposition OF
worn-out muscular tissue.
1t will be seen, then, that the
purpose of the circulation is the
supply everywhere of what is need
ed and the carrying away every
where of what is superfuous and
done with, and the great beauty Of
the process is that the demand for
these changes is the very force
which determines the circulation.
1t is we'll known in chemistry that
substances have an affinity for their
opposites, acids for alkalies, etc.
affinity is a tendency to mix to-
gether.) A similar affinity in the
blood causes it to move towards
parts which are defective in what
it possesses or uperabundant in
what it lacks, and this affinity is
the cause or force which determines
the motion of the blood in the capil-
Iaries; it moves toward that for
which it has an affinity.
We will give only one of the eX-
periments which have been made
i'm illustration of this principle. 1t
has been found possible to place a
portion of the transparent lung of
the frog under the microscope while
the animal is alive, by which the
circulation in the capilaries in that
part can be observed. So long as
the oxygen can be supplied by the
animals breathing, the carbonized
blood moves rapidly towards the
tissues Astounding I'm oxygen, but if
a stream of carbonic acid gas is
made to pass over the part, the cir
culatiOn at once stops, because the
blood and the tissues it circulates i'm
are equally carbonized, and conse-
quently there is no affinity of carbon
for oxygen to promote the motion.
The independence of this capillary
circulation Of the hearts motion is