COURSE OF CIRCULATION IN MAMMALS 



145 



By some it is believed that the right auricle contracts very shortly 

 before the left auricle, and the left ventricle before the right ventricle. 

 Of this period of 0-8 second- 

 Auricular systole occupies about 0-1 second. 



diastole 0-7 



Ventricular systole 0-3 



diastole 0-5 



The sequence and duration of the events happening in the heart, 

 and the pressure inside the heart the endocardiac pressure are 

 studied by means of an instrument termed the " cardiac sound." 

 The sound a two-way tube is pushed down the jugular vein until 



FIG. 53. TRACINGS FROM THE HEART OF A HORSE, BY CHAUVEAU AND MAREY. 



The upper tracing is from the right auricle, the middle from the right ventricle, and 

 the lowest from the apex of the heart. The horizontal lines represent time, 

 and the vertical amount of pressure. The vertical dotted lines mark coincident 

 points in the three movements. The breadth of one of the small squares repre- 

 sents one-tenth of a second. The auricular contraction is less sudden than 

 the ventricular, and lasts only a very short time, as indicated by the line a b. 

 The ventricle, on the other hand, contracts suddenly and forcibly and remains 

 contracted a considerable time, as shown by the line c' d' and by the flat top 

 to the curve which succeeds d'. 



the orifice of one tube lies in the right ventricle, and of the other in 

 the right auricle. The cardiac orifices of the tubes are covered with 

 rubber membrane, beneath which are wire springs set to resist com- 

 pression. The tubes are connected with recording tambours, which 

 write on a moving drum covered with smoked paper. Another 

 tambour may be used to record the cardiac impulse. The aortic 

 pulse curve may also be recorded in other experiments simultane- 

 ously with the left intraventricular pressure. This is effected by 

 pushing the sound down the carotid, so that one tube opened into the 

 aorta and the other into the left ventricle. The tracings so obtained 



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