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(?66 GENERAL PATHOLOGY.
ries are directly affected by the vaso-motor system of nerves. This pro-
duces what is known as variations in "arterial tension." In the condi-
tion of health the blood may be said to be grasped by the muscular coats
of the arteries with a certain degree of force. Therefore the blood is
constantly subjected to a considerable degree of pressure, which is
plainly indicated by the " spirting " Mhen an artery is severed. Bleed-
ing lessens the volume of the blood directly, yet it requires a consider-
able reduction in the volume to very materially reduce the arterial pres-
sure. So too, conversely, the volume of the blood may be doubled by
the process of transfusion before the arterial tension is materially
increased. This equality of the arterial tension is maintained directly
by the nervous system acting upon the muscular coats of the arteries,
through which these vessels are contracted or expanded to accommodate
the changing volume of the blood. This tension in disease is subject to
very wide alterations, and, in the main, these alterations reflect the con-
dition of the nervous system. It is this coincidence of conditions that
gives to the qualities of the pulse their importance. In disease strength
of the heart and tension of the arterial system do not always coincide.
The source of their enervation is different. The heart receives its
supply from the great sympathetic and from ganglia situated within
itself, but principally from the pneumogastric, while the vaso-motor
nerves seem to arise from the spinal cord. Hence, while in many
respects the condition of the heart and arteries may coincide, they do
not do so of necessity.
^1 compressible jmlse is produced by relaxation of arterial tension.
This condition permits the blood to flow through the arterial system
and into the capillaries with less restraint, and, if the heart is strong,
produces a large soft pulse that may be readily compressed. In this con-
dition of the arteries a weak heart will produce a correspondingly small
and quick pulse. The compressibility of the pulse is ascertained by
placing t^vo or more fingers on the artery and exerting more or less
firm pressure until the pulsation is no longer felt under the finger near-
est the distal (or terminal) end of the vessel. The degree of pres-
sure required to do this determines the compressibility. If this is not
accomplished with a reasonable pressure, the pulse is said to be incom-
pressible and marks a strong heart with a fairly high arterial tension,
and indicates a good condition of the system. If this incompressibility
is extreme, as is often the case in the beginning of fevers, sedatives are
called for, and especially so if the pulse is very frequent. In the reverse
case, if the pulse be easily compressible, quick, and very frequent, it
marks a condition of general prostration, and calls for stinmlants, espe-
cially cardiac stimulants, such as digitalis. It will be noted here that
these differences are based on the qualities of the pulse independent of
its frequency. Yet it is a clinical fact that a full strong pulse never
becomes so frequent as the small quick pulse, which is the indication of
dangerous prostration.
A relaxed condition of the arterioles with a heart of only moderate
strength will give a full round pulse that, if not closely observed, might
readily be mistaken for a strong heart-beat. The ease with wliich it
may be compressed ^ill at once correct the error and set the physician