ARREST OF THE HEART'S ACTION. 59 



This experiment shows how completely and promptly the heart, even of a 

 cold-blooded animal, may be arrested in its action by mechanical injury 

 (Flint, 1861). 



Cases of death from engorgement of the heart are not unusual in prac- 

 tice ; and the form of organic disease which most frequently leads to sudden 

 death is that in which the heart is liable to great distention. In other lesions 

 there is not this tendency ; but when the aortic orifice is contracted or the 

 valves are insufficient, any great disturbance of the circulation will cause the 

 heart to become engorged, which is liable to produce a fatal result. 



Most persons are practically familiar with the distressing sense of suffoca- 

 tion which frequently follows a blow upon the epigastrium ; and a few cases 

 are on record of instantaneous death following a comparatively slight concus- 

 sion in this region. Although these cases are rare, they are well recognized, 

 and the effects are generally attributed to injury of the solar plexus. The 

 distress is precisely what would occur from sudden arrest of the heart's ac- 

 tion. It is the blood charged with oxygen which supplies the wants of the 

 tissues, and not the simple entrance of air into the lungs ; and arrest of the 

 circulation of arterial blood, from any cause, produces suffocation as com- 

 pletely as though the trachea were tied. It is a question whether the ar- 

 rest of the heart, if this be the pathological condition, be due to concussion 

 of the nervous centre or to the direct effects of the blow upon the organ it- 

 self. Present data do not afford a definite answer to this question, but they 

 sustain, to a certain extent, the opinion that in such accidents, the symptoms 

 are due to direct injury of the heart. An additional argument in favor of 

 this view is founded on what is known of the mode of operation of the sym- 

 pathetic system. The effects of stimulation or irritation of this system are 

 not instantaneously manifested, as is the case in the cerebro-spinal system, but 

 are developed slowly and gradually. 



As far as the results of experiments are concerned, the nervous influences 

 which arrest the action of the heart seem to operate through the pneumogas- 

 trics and are derived from the spinal accessory nerves. This action can be 

 closely imitated by electricity. The causes of arrest in this way are many and 

 varied. Among them may be mentioned, sudden and severe bodily pain and 

 severe mental emotions. With the exception of arrest of the heart's action 

 from loss of blood and from distention, from whatever cause it may occur, 

 stoppage of the heart takes place from influences operating through . the 

 nervous system. It may be temporary, as in syncope, or it may be permanent ; 

 and examples of the latter, though rare, are sufficiently well authenticated. 



In an animal just killed, as the pulsations of the heart become slower and 

 slower until they are finally arrested, it is constantly observed that the auric- 

 ular appendage on the right side continues to contract for some time after 

 the other portions of the heart have ceased their action. 



