498 



ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1910. 



ones, each the i)i'ecursor 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 



ba 



i 



H,SO< 



Hg 



Inverted image of 



tip of capillary 



X 300 



H.^SO^ 



Via. '1 — Dia,i;i-ain of a hircl haviui; its pulse tal<ou. 



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 



Fig. 3. — Electro-cardiogram of a goldfincli. 



may be gauged. Figure 3 is two seconds' worth of a record taken 

 with a goldfinch arranged in the Avay 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 tliin horizontal line which 



