42 CIRCULATION OF THE BLOOD 



At birth the pulse is 136. It gradually diminishes during the first 

 year to about 128. The second year, the diminution is quite rapid, 107 

 being the mean frequency at two years of age. After the second year, 

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

 its minimum, which is about 70 per minute. At the later periods of 

 life the movements of the heart become slightly accelerated, ranging 

 between 75 and 80. 



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

 rapidity 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 into 

 old age. 



The condition of the digestive system has a marked influence on the 

 rapidity of the pulse, and there usually is an increase of five or 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 ascertained that the pulse is 

 accelerated in a greater degree by animal than by vegetable food. 



It has been observed that the position of the body has a decided 

 influence on the rapidity of the pulse. In the male, there is a differ- 

 ence of about 10 beats between standing and sitting, and 15 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. These are given as averages 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 1 5 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. Nearly the same results as those cited above 

 were obtained in these experiments. In a single observation, the pulse, 

 standing, was 89; lying, 77; difference, 12. With the posture changed 

 without muscular effort, the results were as follows: standing, 87; 

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

 have been offered by physiologists ; but Guy seems to have settled 

 experimentally the fact that the acceleration is due in part to the 



