THE ACTION OF THE HEART 353 



the habit of looking upon the augmentor mechanism as affording a 

 fairly steady background of augmentor excitation upon which 

 the inhibitory mechanism may play in delicate adjustment to the 

 needs of the circulation. .There is a perceptible quickening of 

 the beat with any muscular movement, at least with any as ex- 

 tensive as that required to press a telegraph key. The quickening 

 shows itself in the next beat after the beginning of the movement. 

 The suggestion has been made that during the discharge of the 

 exciting nervous impulses from the brain to the muscles, there is 

 irradiation in the brain stem unto the inhibitory center; that this 

 irradiation depresses the center, and so allows a quickening of the 

 beat. 



There are certain conditions in which the augmentor center 

 seems to show heightened activity. After muscular exercise there 

 is a more or less persistent acceleration of the heart that appears 

 to be due to stimulation of the augmentor center by the waste 

 products of muscular activity which persist for a time in the cir- 

 culating blood. The acceleration of the heart in time of emotional 

 stress or of great pain is to be explained, as stated previously, 

 through the connection of the augmentor mechanism with the 

 thoracico-lumbar autonomic, the emergency, system. 



The familiar changes of heart-rate with changes of posture, 

 slowed when lying, quickened with sitting or standing, are ap- 

 parently the results of the redistribution of the blood over the 

 Body under the influence of gravity. The quickening of the beat 

 when one stands erect is undoubtedly an adaptation designed to 

 overcome the tendency of the blood to accumulate in the lower 

 parts of the Body when in this position; but how the adaptation 

 is brought about is not known. Successive swallowing, as in sip- 

 ping water, increases the heart-rate by depressing the inhibitory 

 center. A blow over the stomach (the solar plexus) gives rise to 

 afferent impulses which stimulate the inhibitory center; the heart- 

 rate is therefore diminished. 



These are all illustrations of the general rule that the heart- 

 beat may be modified by sensory stimulations. It is a matter of 

 ordinary observation that many experiences, particularly those 

 involving sensory impressions of high intensity, are accompanied 

 by marked changes in heart-rate. 



In connection with this analysis of the control of the heart- 



