ON THE SPHYGMOGRAPH, OPv PULSE-RECORDER. 
139 
the day ; and, supposing that each man has eight hours’ sleep in 
the twenty-four, he may be said to rest during one-third of his 
existence. If the pulse were always to beat at a rate of 62 a 
minute, then, as the systole occupies one-third of the beat, the 
period of the heart’s repose during the life of the individual 
would be two- thirds of its length. 
Again, there are two ways in which the wager to walk a 
thousand miles in the same number of hours may be laid. 
Either the total number of miles must be completed in the 
time, with no restrictions as to the manner in which they are 
done ; or it may be required that a mile should be walked in 
each of the hours. This last case is more strictly analogous 
to the action of the heart. The period of work is short, and 
that of repose is short also ; but both are frequent. No time 
for prolonged rest is allowed, so all nutrition by the blood in 
the coronary vessels must be done intermittently, just as the 
pedestrian, in the second of the above-cited instances, is wise if 
he distributes his meals over his sitting intervals, instead of 
taking them in large quantities less frequently. What the 
above given law means is that, according to the differences in 
the length of the repose or diastole, so is that of the cardiac 
contraction modified ; or again, referring to the analogy of the 
pedestrian : suppose that when walking a thousand miles, one in 
each hour, he could get over each mile in twenty minutes, then 
if he had to do the same distance in 1,500 hours, one in each 
hour and a half, he would get over each mile in a less time — 
say fifteen minutes — because the longer period of rest would 
make walking so much the less difficult. m But it will be 
remarked that the length of the systole is greater and not less 
when the diastole is longer. This is perfectly true, but it does 
not alter the above-stated nature of the problem, because there 
is a peculiarity in the heart’s action which is not found in that 
of the walking man. 
The law which regulates the frequency of the pulse is not a 
simple one ; but it partly depends on the influence exerted by 
the changes which occur in the calibre of the smaller arteries 
of the skin ; the pulse being quick when these vessels, which 
have muscular walls, are very open, and slow, when they are 
contracted ; so that when anyone blushes the pulse augments 
in rapidity, on account of the dilatation of the small ves- 
sels ; and when the skin gets pale with cold the pulse is 
retarded. From these remarks it is evident that when the 
pulse is quick the blood escapes from the arterial system into 
the capillaries more quickly than when it is slow. Conse- 
quently, the difficulty which the heart must experience 
in emptying itself into the arteries varies according to the 
rapidity of the pulse ; and as during the diastole which pre- 
ceded any systole under consideration, it was supplied with 
