FREQUENCY OF THE HEART'S ACTION. 49 



the frequency progressively diminishes until adult life, when it is at its min- 

 imum, which is about 70 per minute. At the later periods of life the move- 

 ments of the heart become slightly accelerated, ranging between 75 and 80 

 (Guy). 



During early life there is no marked and constant difference in the rapid- 

 ity of the pulse in the sexes ; but near the age of puberty, the development 

 of the peculiarities relating to sex is accompanied with an acceleration of the 

 heart's action in the female, which continues even into old age. 



Influence of Digestion. The condition of the digestive system has a 

 marked influence on the rapidity of the pulse, and there is generally an 

 increase in the pulse of between five and ten beats per minute after each 

 meal. Prolonged fasting diminishes the frequency of the pulse by about 

 twelve beats. Alcohol first diminishes and afterward accelerates the pulse. 

 Coffee is said to accelerate the pulse in a marked degree. It has been ascer- 

 tained that the pulse is accelerated to a greater degree by animal than by 

 vegetable food. 



Influence of Posture and Muscular Exertion. It has been observed that 

 the position of the body has a very marked influence upon the rapidity of the 

 pulse. In the male, there is a difference of about ten beats between standing 

 and sitting, and fifteen beats between standing and the recumbent posture. 

 In the female, the variations with position are not so great. The average is, 

 for the male standing, 81 ; sitting, 71 ; lying, 66 ; for the female : standing, 

 91 ; sitting, 84 ; lying, 80. This is given as the average of a large number 

 of observations. There were a few instances, however, in which there was 

 scarcely any variation with posture, and some in which the variation was 

 much greater than the average. In the inverted posture, the pulse was found 

 to be reduced about fifteen beats (Guy). 



The question at once suggests itself whether the acceleration of the pulse 

 in sitting and standing may not be due, in some measure, to the muscular 

 effort required in making the change of posture. This is answered by the 

 experiments of Guy, in which the subjects were placed on a revolving board 

 and the position of the body was changed without any muscular effort. The 

 same results as those cited above were obtained in these experiments, showing 

 that the difference is due to the position of the'body alone. In a single obser- 

 vation, the pulse, standing, was 89; lying, 77; difference, 12. With the post- 

 ure changed without any muscular effort, the results were as follows : stand- 

 ing, 87 ; lying, 74 ; difference, 13. Different explanations of these variations 

 have been offered by physilogists ; but Guy seems to have settled experi- 

 mentally the fact that the acceleration is due in part to the muscular effort 

 required to maintain the body in the sitting and standing positions. The 

 following are the results of experiments bearing on this point, in which 

 it is shown that when the body is carefully supported in the erect or sitting 

 posture, so as to be maintained without muscular effort, the pulse is less 

 frequent than when the subject is standing ; and farthermore, that the pulse 

 is accelerated, in the recumbent posture, when the body is imperfectly sup- 

 ported : 



