498 



ANNUAL EEPOKT SMITHSONIAN INSTITUTION, 1910. 



ones, each the precursor of a ventricular systole, are easiest to count 

 when recorded. To record the movements the image of the tip of 

 the tube is magnified some three hundred times, and the boundary 



b> 



I 



H. i S0 4 



Hg 



Inverted image of 



tip of capillary 



X 300 



H a S0 4 



Pig. 2 — Diagram of :i bird having i(s pulse taken. 



between mercury and acid is photographed on a moving plate on 

 which is simultaneously projected the shadow of one end of a tun- 

 ting fork vibrating at a known rate, so that the speed of the plate 



Pig. 3. — Electrocardiogram of a goldfinch. 



may be gauged. I^igure 3 is two seconds' worth of a- record taken 

 with a goldfinch arranged in the way shown diagrammatically in 

 figure 2. The tracing of a tuning fork vibrating one hundred times 

 a second is seen above, and a thick and a thin horizontal line which 



