126 HANDBOOK OF PHYSIOLOGY. 



caused by the vibrations consequent on the tightening and closure of the 

 auriculo-ventricular valves. 



The method thus described may, as a rule, demonstrate quite cor- 

 rectly the variations of endocardial pressure, and these variations only, 

 but there is a danger lest the muscular walls should grip the air-bags, 

 even after the complete expulsion of the fluid contents of the chamber, 

 and if so the lever would remain at its highest point for too long a time. 

 The highest curve under such circumstances would represent on the 

 tracing not only, as it ought to do, the endocardiac pressure, but also in 

 addition the muscular pressure exerted upon the cardiac sound itself. 

 (M. Foster.) 



Frequency and Force of the Heart's Action. 



The heart of a healthy adult man contracts from seventy to seventy- 

 five times in a minute ; but many circumstances cause this rate, which 

 of course corresponds with that of the arterial pulse, to vary even in 

 health. The chief are age, temperament, sex, food and drink, exercise, 

 time of day, posture, atmospheric pressure, temperature. 



(1.) Age. The frequency of the heart's action gradually diminishes 

 from the commencement to near the end of life, but is said to rise again 

 somewhat in extreme old age, thus : 



Before birth the average number of pulsations per minute is 150 



Just after birth, from 140 to 130 



During the first year, , . . . 130 to 115 



During the second year, .... 115 to 100 



During the third year, 100 to 90 



About the seventh year, .... 90 to 85 



About the fourteenth year, the average number 



of pulses in a minute is from . . . 85 to 80 



In adult age, 80 to 70 



In old age, 70 to 60 



In decrepitude, 75 to 65 



(2.) Temperament and Sex. In persons of sanguine temperament, 

 the heart acts somewhat more frequently than in those of the phleg- 

 matic ; and in a female sex more frequently than in the male. 



(3 and 4.) Food and Drink, Exercise. After a meal the heart's ac- 

 tion is accelerated, and still more so, during bodily exertion or mental 

 excitement ; it is slower during sleep. 



(5.) Diurnal Variation. In the state of health, the pulse is most 

 frequent in the morning, and becomes gradually slower as the day ad- 

 vances : and that this diminution of frequency is both more regular and 

 more rapid in the evening than in the morning. 



(6.) Posture. The pulse, as a general rule, especially in the adult 

 male, is more frequent in the standing than in the sitting posture, and 

 in the latter than in the recumbent position ; the difference being great- 

 est between the standing and the sitting postures. The effect of change 

 of posture is greater as the frequency of the pulse is greater, and, ac- 

 cordingly, is more marked in the morning than in the evening. By 

 supporting the body in different positions, without the aid of muscular 



