98 A MANUAL OF PHYSIOLOGY 



whose arteries have been rendered less extensible by the deposit 

 of lime-salts in their walls (atheroma), and in cases where the 

 orifice of the aorta has been narrowed from disease of the semi- 

 lunar valves (aortic stenosis). Since these conditions are in 

 general associated with hypertrophy and dilatation of the left 

 ventricle, the slow emptying of the ventricle is partly due to the 

 greater quantity of blood which it contains. In whatever way 

 the delay in the emptying of the ventricle is brought about, the 

 most probable explanation of the anacrotic pulse is that the 

 delay affords time for one or more secondary waves to be de- 

 veloped in the arterial system before the summit of the curve 

 has been reached, and that these are superposed upon the long- 

 drawn primary elevation. In aortic insufficiency, where the left 

 side of the heart is never cut off entirely from the aorta, the 

 auricular impulse is sometimes marked on the pulse-curve as a 

 distinct elevation ; and this gives rise to a peculiar kind of 

 anacrotic pulse, especially in the arteries nearest the heart 

 (Fig. 32, F). 



Frequency of the Pulse. In health, the working of the cardiac 

 pump is so smooth and apparently so self-directed, that it 

 needs a certain degree of attention to perceive that the rate of 

 the stroke is not absolutely constant. It is, in reality, affected 

 by many internal conditions and external influences. 



At the end of foetal life the rate is given as 144 to 133; from 

 birth till the end of the first year, 140 to 123 ; from 10 to 15 years, 

 91 to 76 ; from 20 to 25 years, 73 to 69. It remains at this till 60 

 years, and increases again somewhat in old age.* At all ages 

 the pulse is somewhat quicker in the female than in the male, 

 the excess amounting to about 8 beats a minute. So that if 

 we take the average rate for a man (in the sitting position) as 

 72, the average for a woman will be 80. The difference is partly 

 due to the fact that the average man is taller than the average 

 woman ; and it is known that in persons of the same sex and age 

 the pulse-rate has an inverse relation to the stature. But 

 there may be, in addition, a real sexual difference. It must not 

 be forgotten that a small number of perfectly healthy persons 

 have an habitually slow pulse, not above 50 in the minute. The 

 position of the body exercises a slight, but relatively constant, 



* It must be remembered that these numbers are merely averages. 

 Some healthy individuals have a much lower pulse-rate than 72 per minute, 

 and some a rate considerably greater. Thus, while the average pulse-rate 

 (taken in the sitting position) of 87 healthy (male) students (in the writer's 

 laboratory), whose ages ranged from 1 8 to 36 years, was 73, the extreme 

 variation was from 54 to 98. In the standing position the average was 

 80, and the variations 64 to 105. In the supine position, average 69, and 

 variations 48 to 98. After a short spell of muscular exercise (generally 

 running up and down some flights of stairs) the average in the standing 

 position was 119, the variations 75 to 164, and the average increase 32. 



