134 THE CIRCULATION. 



diaphragm. The production of the impulse is, perhaps, 

 further assisted by the tendency of the aorta to straighten 

 itself and diminish its curvature when distended with the 

 blood impelled by the ventricle ; and, by the elastic recoil 

 of all the parts about the base of the heart, which, accord- 

 ing to the experiments of Kurschner, are stretched down- 

 ward and backward by the blood flowing into the auricles 

 and ventricles during the dilatation of the latter, but re- 

 cover themselves when, at the beginning of the contraction 

 of the ventricles, the flow through the auriculo- ventricular 

 orifices is stopped. But these can only be accessory con- 

 ditions in the perfect state of things ; for the same tilting 

 movement of the heart ensues when its apex is cut off, and 

 no tension or change of form can be produced by the blood. 



Frequency and Force of the Heart's Action. 



The frequency with which the heart performs the actions 

 we? have described, may be counted by the pulses at the 

 wrist, or in any other artery ; for these correspond with 

 the contractions of the ventricles. 



The heart of a healthy adult man in the middle period 

 of ]ife, acts from seventy to seventy-five times in a minute. 

 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 : 



In the embryo the average number of pulses in a 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 . . . . . . . 7 to 60 



In decrepitude 75 to 65 



In persons of sanguine temperament, the heart acts 



