THE CIRCULATION OF THE BLOOD AND LYMPH 95 



with hypertrophy and dilatation of the left ventricle, the 

 slow emptying of the ventricle is, perhaps, 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 developed 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. 27, 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 144-133 ; from 

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

 years, 91-76 ; from 20 to 25 years, 73-69. 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 



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

 Some healthy individuals have a much slower 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, 

 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 varia- 

 tions 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. 



