50 CIRCULATION OF THE BLOOD ACTION OF THE HEART. 



" 1. Difference between the pulse in the erect posture, without support, 

 and leaning in the same posture, in an average of twelve experiments on the 

 writer, 12 beats ; and on an average of eight experiments on other healthy 

 males, 8 beats. 



" 2. Difference in the frequency of the pulse in the recumbent posture, 

 the body fully supported, and partially supported, 14 beats on an average of 

 five experiments. 



" 3. Sitting posture (mean of ten experiments on the writer), back sup- 

 ported, 80 ; unsupported, 87 ; difference, 7 beats. 



" 4. Sitting posture with the legs raised at right angles with the body 

 (average of twenty experiments on the writer), back unsupported, 86 ; sup- 

 ported, 68 ; difference, 18 beats. An average of fifteen experiments of the 

 same kind on other healthy males gave the following numbers : back unsup- 

 ported, 80 ; supported, 68 ; a difference of 12 beats." 



Influence of Exercise etc. Muscular exertion increases the frequency of 

 the pulsations of the heart ; and the experiments just cited show that the 

 difference in rapidity, which is by some attributed to change in posture some 

 positions, it is fancied, offering fewer obstacles to the current of blood than 

 others is mainly due to muscular exertion. According to Bryan Robinson 

 (1734), a man in the recumbent position has 64 pulsations per minute; 

 sitting, 68 ; after a slow walk, 78 ; after walking four miles in an hour, 100 ; 

 and 140 to 150 after running as fast as he could. This general statement, 

 which has been repeatedly verified, shows the important influence of the 

 muscular system on the heart. 



The influence of sleep upon the action of the heart reduces itself almost 

 entirely to the proposition that during this condition, there is usually en- 

 tire absence of muscular effort, and consequently the number of beats is less 

 than when the individual is aroused. It has been found that there is no 

 difference in the pulse between sleep and perfect quiet in the recumbent post- 

 ure. This fact obtains in the adult male ; but there is a marked difference 

 in females and young children, the pulse being always slower during sleep 

 (Quetelet). 



Influence of Temperature. The influence of extremes of temperature 

 upon the heart is very decided. The pulse may be doubled by remaining a 

 very few minutes exposed to extreme heat. Bence Jones and Dickinson have 

 ascertained that the pulse may be very much reduced in frequency, for a 

 short time, by the cold douche. It has also been remarked that the pulse is 

 habitually more rapid in warm than in cold climates. 



Although many circumstances materially affect the rapidity of the heart's 

 action, they do not complicate, to any great extent, examinations of the pulse 

 in disease. In cases which present considerable febrile movement, the pa- 

 tient is generally in the recumbent posture. The variations induced by vio- 

 lent exercise are easily recognized, while those dependent upon temperature, 

 the condition of the digestive system, etc., are so slight that they may prac- 

 tically be disregarded. It is necessary to bear in mind, however, the varia- 

 tions which exist in the sexes and at different periods of life, as well as the 



