The San Francisco call., 1903-12-31
Tubes IN the Body.
BY W. R. c. LArsoN. NJ d.

editor Health culture magazine new lNih. }
Copyright 1905, by Joseph b Bowles.
Among. the most remarkable and
beautiful structures of the body are the
blood tubes-the system of piping by
means OF which the blood is conveyed
from the heart to the tissues. through
the tissues themselves and then back TO
the heart. OF the heart itself. that Won
derful double pump. to the action of
which the flow of the blood is mainly
due, and Of the blood the center and
intermediary of all life processes, we
have written in previous articles.
The tubes conveying the blood from
the heart are called arteries. And the
structure Of these tubes is peculiarly
adapted to the work they have to do.
In discussing the hearts action it was
stated that the heart contracted about
seventy times each minute. At each Of
these contractions it throws into the
arteries which go to the tissues about
$50 cubic centimeters, or neardly six
ounces Of blood. Now if the artery
were a hard, unyielding tube. like a
lead gas pipe or a clay water main, it
would require great force to keep the
blood moving through the three or four
feet of tubing which lie between the
heart and the more distant tissues But
the artery is far from being rigid. It's
walls are very strong and very elastic,
much more so than ordinary rubber
tubing. SO when the quick contraction
of the left ventricle throws tumbler-
full of blood into the arteries they ex-
pand to take it in, and then by their
own elasticity they contract again.
The blood once in the artery cannot
get back into the heart because of the
closing of the aortic valve. which
guards the opening of the large artery
leading from the heart TO the tissues.
SO as the artery contracts again TO it's
natural caliber the blood thrown into
il from the heart is passed on in a kind
Of wave. This elastic expansion and re-
coil Of the arteries is a most powerful
assistance to the heart in propelling
the blood through the body. And it is
in this alternate enlargement and con-
traction Of all the arteries, once for
each closing up of the heart, that
causes what is called the pulse. The
pulse may be felt at the wrist, the
temple, in the groin, under the arm or
at any other point where an artery
passes sufficiently near the surface to
be felt by the finger.
In the disease known as old age
Capillary fibrosis) there is
change in the nature Of the material
composing the walls of the arteries and
capillaries, which causes them to lose
their power Of elestic response to the
heart impulse This condition is event
ually fatal in every case, thus showing
the importance of the arterial expan-
sion and recoil.
Not only, however, must the artery
be elastic; it must be strong-strong
enough to withstand a pressure which
at one point is equal to column of
mercury eight inches high And the
structure OF the artery is such as to
insure the highest possible degree of
those two qualities strength and elias
ticity The arterial walls are COM
posed Of several coats or layers. In
side these is a thin layer of cpithelial
cells (called here endOtheliaD These
are of irregular shape, and are Joined
together at the edges by a kind of
cement. Outside of this lies the prin-
cipal coat of the artery itself, COM
posed Of several layers, the most i'm
portant Of which is made up of tiny
muscle cells. which pass round the cali
ber of the artery and impart tc it that
combination of elasticity ana strength
which is so important to its functions.
Each of these tiny snakelike muscle
cells is a minute muscle IN some Of
the arteries these muscles have a spe-
cial set Of nerves, which regulate the
caliber Of the blood tube, causing it at
one time to contract, causing pallor and
coldness of that part Of the body, and
under other circumstances 70 expand,
thus containing more blood and result
ing in added heat to the part, with
flushing.
From the heart the blood passes into
one large artery called the aorta. The
aorta gives off a number of smaller
branches. and these give off still small
er branches, which again subdivide,
and so on, until the smallest arteries,
called arteriols, are reached.
The blood stream returns from the
tissues to the heart through blood tubes
which differ widely from the arteries
just described. The arterial blood flow
ing from the heart is under strong
pressure, and is sent forth IN powerful
and rapid jets. To withstand this pres
sure the arteries must be strong and
elastic. But the blood going back to
the heart is under but little pressure.
and the flow is steady. Therefore the
blood tubes leading to the heart (the
veins) need not be, and are not, as
strong nor as elastic as the arteries.
Like the artery, the vein is a tube con-
sisting Of a number of layers which.
however, we may roughly divide into
inner and outer, the inner composed of
endothelial and the outer of muscle
cells. The walls of the veins are much
thinner than those of the arteries, and
there is no pulsation or throbbing in