242 ANIMAL PHYSIOLOGY. 
blood would pass through the heart in about thirty beats, or 
in less than half a minute. 
When we calculate the work done by the heart for certain 
intervals, as the day, the week, month, year, and especially for 
a moderate lifetime, and compare this with that of any ma- 
chine it is within the highest modern skill to construct, the 
great superiority of the vital pump in endurance and working 
capacity will be very apparent; not to take into the account at 
allits wonderful adaptations to the countless vicissitudes of life, 
without which it would be absolutely useless, even destructive 
to the organism. 
Some of these variations in the working of the heart we may 
now to advantage consider. 
“VARIATIONS IN THE CARDIAC PULSATION. 
These may be ascertained either by the investigation of the 
arteries or of the heart, for every considerable alteration in the 
working of the heart expresses itself also through the arterial 
system. In speaking of the pulse, the reference is principally 
to the arteries, but in each case we may equally well think of 
the heart primarily as acting upon the arteries. 
1. The frequency of the heart-beat varies, as might be sup- 
posed, with a great multitude of conditions, the principal of 
which are: age, being most frequent at birth, when it may be 
140 per minute, gradually slowing to old age, when it may fall 
to 60. In feeble old age the heart-beat may, like many other of 
the functions of the body, approximate the infantile condition, 
being very frequent, small, feeble, and easily disturbed in its 
rhythm. 
It is a matter of no small importance to the medical student 
to be aware of the normal rate for different periods of life, 
hence we give below a pretty full statement of the variations 
with age. It will be understood that the numbers are only ap- 
proximative, and that large allowance must be made for indi- 
vidual deviations: 
At birth, 130-140 At 4 years, 96-94 At 20 years, 78-72 
lyear, 120-1830 ° 5 “ 9490 30 “ %5-70 
2 years, 100-110 10 “ 90-85 50 “ 70-65 
3 “ 100- 96 15 * 80-%5 
Sex.—The cardiac beat is more frequent in females; stature, 
more frequent in the short; postwre, most rapid in the standing 
position, slower when sitting, and slowest in the recumbent 
