ROY'S FROG HEART TONOMETER 



135 



lever near the axis and bending it over, so as to lie to the other side of the 

 axis, and thus act as a counterpoise. To its end a small weight can be hung, 

 as, for instance, a piece of folded paper, whose position can be varied until 

 the best amplitude is obtained. 



Fig. 105 shows tracings taken by this lever. Tracings i and n are 

 taken with the lever resting on the ventricle only, in n the drum 

 moving rather more than twice as fast as in i. The up-stroke means 

 a contraction of the heart, the down-stroke relaxation. At the end of 

 relaxation there is a pause for a time before a fresh contraction occurs, 

 and in a few of these a slight rise is indicated, which is due to the 

 filling of the ventricle on auricular systole. The contraction is seen 

 to be sustained for a time before relaxation occurs. In tracings in 

 and iv the lever was placed so as to rest on the junction of auricle 

 and ventricle ; we see that the two contractions are now recorded. 



Eecording by this method we may study any of the results to 

 be obtained in the experiments in which we used the suspension 

 method. 



Another method of recording changes in the excised heart's activity 

 is the plethysmographic method. 



Experiment 2. — Take a tracing with Roy's tonometer, fig. 106. This 

 consists of a small glass bell-jar whose base fits on a brass support. The 

 joint is made tight by smearing the ground surface of the run of the glass 

 vessel with lard and rubbing it down tightly on to the brass base. In the 



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Fig. 106.— Roy's Tonometer. (Halliburton.) 



base is a central hole into which a short cylinder is screwed, and the lower 

 orifice fo this is closed with peritoneal membrane. A second orifice is fitted 



