INFLUENCE OF EXERCISE AND TEMPERATURE. 53 



any muscular effort. The same results as those cited above were obtained in these ex- 

 periments, showing that the difference is due to the position of the body alone. In a 

 single observation, Dr. Guy found the pulse, standing, to be 89 ; lying, 77 ; difference, 

 12. "With the posture changed without any muscular effort, the results were as follows : 

 standing, 87 ; lying, 74 ; difference, 13. Various theoretical explanations of these vari- 

 ations have been offered by physiologists ; but Dr. 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 which bear conclusively 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 only partially supported : 



"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 supported, 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 ; supported, 68 ; difference, 18 

 beats. An average of fifteen experiments of the same kind on other healthy males gave 

 the following numbers: back unsupported, 80; supported, 68; a difference of 12 beats." 



Influence of Exercise, etc. It is a fact generally admitted that muscular exertion in- 

 creases 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. Every one knows, indeed, that the action of the heart 

 is much more rapid after violent exertion, such as running, lifting, etc. Experiments on 

 this point date from quite a remote period. Bryan Robinson, who published a treatise 

 on the "Animal Economy" in 1734, states, as the result of observation, that 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 powerful 

 influence of the muscular system on the heart. The fact is so familiar that it need not 

 be farther dwelt upon. 



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

 the proposition that, during this condition, we have an entire 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 posture. This fact obtains in the adult male ; but it is said by Quetelet 

 that there is a marked difference in females and young children, the pulse being always 

 slower during sleep. 



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, our examinations of the pulse in disease. In 



