Cfi. XX.] ENDOCARDIAC PRtiSStfREl; 24! 



tube of the recording tambour in one's mouth, and holding the 

 breath though keeping the glottis open. The chest then acts 



Fig. 240. Cardiogram from human heart. The variations in the individual beats are due 

 to the influence of the respiratory movements on the heart. To be read from left to 

 right. 



as the first tambour, and the movements of the lever (cardio- 

 pneumatogram) may be written in the usual way. 



Endocardiac Pressure. 



The tracings of the cardiograph are, however, very variable, 

 and their interpretation is a matter of discussion. ' A much better 

 method of obtaining a graphic record of the events of the cardiac 

 cycle consists in connecting the interior of an animal's heart with 

 recording apparatus. 



There are several methods by which the endocardiac pressure 

 may be recorded. 



By placing two small india-rubber air-bags or cardiac sounds 

 down the jugular vein into the interior respectively of the right 

 auricle and the right ventricle, and a third in an intercostal space 

 in front of the heart of a living animal (horse), and placing these 

 bags, by means of long narrow tubes, in communication with 

 three tambours with levers, arranged one over the others in con- 

 nection with a registering apparatus (fig. 241), Chauveau and 

 Marey were able to record and measure the variations of the 

 endocardiac pressure and the comparative duration of the con- 

 tivi. tions of the auricles and ventricles. By means of the same 

 apparatus, the synchronism of the impulse with the contraction 

 of the ventricles is also shown. 



In the tracing (fig. 242), the intervals between the vertical 

 liiu-s represent periods of a tenth of a second. The parts on 

 which any given vertical line falls represent simultaneous events. 

 It will be seen that the contraction of the auricle, indicated by the 

 marked curve at A in the first tracing, causes a slight increase of 



K.P. B 



