FREQUENCY OF THE HEARTHS BEATS. 655 



is well known, and is indicated by their title. It is alleged that the 

 pulse is more accelerated after breakfast than after dinner. Absti- 

 nence and starvation lower its frequency, so also does the prolonged 

 use of a vegetable diet, or the drinking copiously of water. Muscular 

 exertion increases the number of the heart's beats, an alternate con- 

 traction and relaxation of the muscles, having a greater effect than a 

 continuous contraction ; it also increases the respiration. Posture has 

 a remarkable influence, evidently dependent on the muscular effort 

 expended in maintaining different positions of the body ; thus, the 

 beats of the heart are slowest in the recumbent, somewhat quicker in 

 the sitting, and most frequent in the standing, posture. The increase 

 per minute, produced by the change from the recumbent to the sitting 

 position, is 6, and from the latter to the standing posture 9 more, i. e. 

 a difference of 15 occurs between the lying and standing positions. 

 The effect of posture is greater in the morning than in the evening, 

 and it is greater also when the pulse is quick than when it is slow, the 

 difference resulting from the change between lying down and standing 

 being 9 only, when the pulse is 60, 15 when the pulse is 80, and 27 

 when the pulse is already 100 (Guy). That the increase in the heart's 

 beats, from change of posture, is due to muscular effort, is shown by 

 placing a person in the recumbent position on three chairs, and then 

 removing the central one, when the pulse immediately rises, although 

 the horizontal position is still maintained ; whereas, in a person fas- 

 tened to a revolving board, and moved into the erect posture, without 

 effort of his own, no such elevation of the pulse takes place. The 

 frequency of the heart's action undergoes changes coincident with the 

 seasons, being greater in spring and summer than in autumn or winter. 

 The rapidity of the heart's action is also influenced by the hour of 

 the day, being always quicker in the morning, and somewhat retarded 

 towards evening, other conditions as to health, food, and the state of 

 the body being equal ; this difference depends, doubtless, on the gradual 

 exhaustion of the powers of the system during the day's work, and 

 on the recovery of power by the rest obtained at night ; it may partly 

 explain, why the pulse is more accelerated after breakfast than after 

 dinner. During fasting, the pulse exhibits three periods of increased 

 rapidity, and three periods of descent in the twenty-four hours ; thus, 

 it rises from midnight to 2 A.M., from 10 to 11 A.M., and from 2 to 6 

 P.M. ; whilst it falls from 3 to 4 A.M., from 1 to 2 P.M., and from 6 to 

 8 P.M. The joint effect of the time of day and of food, is illustrated 

 by the fact that the pulse, though progressively decreasing from two 

 hours after breakfast to from 3 to 5 in the morning, exhibits fluctua- 

 tions after each meal, so that four maximum, and four minimum, 

 points are noticeable daily. The difference between the highest and 

 lowest points, varies from fourteen to thirty-four pulsations. The 

 minimum points are all observed before meals, the maximum points 

 about two hours afterwards, the greatest increase being after breakfast. 

 External temperature and its concomitant effects on the body, also 

 influence the beats of the heart most materially, an elevation of tem- 

 perature increasing, and a gradual lowering of the temperature dimin- 

 ishing, their frequency, as is illustrated by the exciting effect of a 



