122 HAND-BOOK OF PHYSIOLOGY 



represent on the tracing not only, as it ought to do, the auricular or 

 ventricular pressure on the blood, but, also afterward, the muscular pres- 

 sure exerted upon the bags themselves. (M. Foster.) 



FREQUENCY AND FORCE OF THE HEART'S ACTION. 



The heart of a healthy adult iran 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. 



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 pulses in a minute is 150 



Just after birth . . . . . from 140 to 130 



During the first year . . . " 130 " 115 



During the second year " 115 t( 100 



During the third year " 100 " 90 



About the seventh year . . . . " 90 " 85 

 About the fourteenth year, the average 



number of pulses in a minute is " 85 " 80 



In adult age " 80 " 70 



In old age " 70 " 60 



In decrepitude " 75 " 65 



Temperament and Sex. In persons of sanguine temperament, the 

 heart acts somewhat more frequently than in those of the phlegmatic; 

 and in the female sex more frequently than in the male. 



Food and Drink. Exercise. After a meal its action is accelerated, 

 and still more so during bodily exertion or mental excitement; it is slower 

 during sleep. 



Diurnal Variation. It appears that, in the state of health, the pulse 

 is most frequent in the morning, and becomes gradually slower as the day 

 advances, and that this diminution of frequency is both more regular 

 and more rapid in the evening than in the morning. 



Posture. It is found that, as a general rule, the pulse, especially in 

 the adult male, is more frequent in the standing than in the sitting pos- 

 ture, and in the latter than in the recumbent position; the difference 

 being greatest between the standing and the sitting posture. The effect 

 of change of posture is greater as the frequency of the pulse is greater, 

 and, accordingly, is more marked in the morning than in the evening. 

 By supporting the body in different postures, without the aid of mus- 

 cular effort of the individual, it has been proved that the increased fre- 

 quency of the pulse in the sitting and standing positions is dependent 

 upon the muscular exertion engaged in maintaining them; the usual 

 effect of these postures on the pulse being almost entirely prevented when 

 the usually attendant muscular exertion was rendered unnecessary. (Guy.) 



