ON THE SPHTGMOGRAPH, OR PULSE-RECORDER. 
129 
disposed, that the blood could flow through it only in one 
direction; and from the arrangement of the valves in the 
veins, proved that there was only one course for the blood in 
them also, from which he was led to enunciate the great 
problem of the existence of a circulation of the blood from the 
heart, through the arteries and into the veins, before it was 
proved that there were any direct means of communication 
between these two latter. When the microscope came into use, 
the truth of there being a circulation of the blood was verified by 
the discovery of the capillary system, a network of vessels, far too 
minute to be seen by the unaided eye, which placed the arterial 
in direct connection with the venous system of blood-vessels. 
The blood being therefore pumped by the heart into the 
arteries, is sent into them in jerks or intermittent streams, just 
in the same way that water leaves the spout of an ordinary 
pump that is not being worked quickly. The arteries, how- 
ever, being elastic, yield to the pressure of each stroke, part of 
the force of which is therefore spent in distending them, part* 
in sending the blood onward. There being an interval between 
each two beats, the force stored up in the distended elastic 
arteries during the contraction of the heart is employed in aiding 
the onward blood-stream during the interval in which it rests ; 
and as a consequence of this the flow of the blood becomes less 
and less jerky in the arteries further and further from the 
heart, until in the capillaries, and therefore in the veins also, 
the stream is quite uniform. 
It is the above-mentioned jerkiness of the blood-flow in the 
arteries which produces the phenomenon known as the pulse ; 
and as there are arteries of considerable size in most parts of 
the body, the pulse is to be felt wherever these vessels are 
sufficiently superficial. On either side of the wrist there is an 
artery which can be found with facility, that on the thumb side 
being the one most easily reached and most readily felt. 
^Besides these, the carotid in the neck, the temporal not far 
above the outer end of the eyebrow, and the digital arteries 
along the sides of the fingers, are perhaps the most conve- 
nient for observation. 
On placing the finger on one of these arteries, the sensation 
of an intermittent rise and fall is felt beneath it, which is 
termed the pulse, each rise closely following the pulsation 
against the chest-wall produced by the heart at the commence- 
ment of its contraction. In almost all cases nothing more is felt, 
but very attentive observation makes it evident that the 
impulse is abrupt, and that the following fall is slow. Some 
pulses appear to be much more ample than others, and differ- 
ences in the rapidity of the heart’s action are the most easy to 
be detected. 
VOL. XIII. — NO. LI. K 
