THE PHYSIOLOGY OF MUSCULAR WORK 231 



The figures for the pulse in the last table are certainly somewhat 

 under-estimated, for it was not possible to take all the observations 

 immediately after the march ; the rate of the pulse begins to de- 

 crease directly the work is at an end, and this is especially the case 

 in the well-trained man. 



These results represent the condition which probably obtains 

 in active healthy men of the physique of the ordinary infantry 

 soldier ; the men were not picked men, and the data are not to 

 be considered as rigidly exact, for it was not always possible to 

 guard against the influence of nervousness in the first examination 

 and of a brief rest directly after marching. 



The next table gives the results of observations in the pulse 

 of healthy men before and after running : 



The heart beats more quickly during muscular work. The 

 object is clear, but the means whereby it is attained are complex. 

 It has already been shown that a more rapid circulation is necessary 

 to meet the various demands of muscular activity : the blood sup- 

 plies these needs, and the heart is the pump which forces it to 

 circulate through the various parts. The adjustment begins with 

 the performance of work, and it is necessary to study the means 

 whereby this is brought about. 



The heart and the arterioles are under the control of the nervous 

 system ; by the action of the vagus nerve the beats become slower ; 

 they are quickened by impulses passing down the sympathetic 

 nerve. During rest the vagus nerve appears to exert a constant 

 inhibitory action upon the heart, but directly impulses pass from 



