402 



ELECTRO-PHYSIOLOGY 



CHAP. 



corresponding displacement of the mercury meniscus. The 

 quicksilver in the capillary responds even to excessively rapid 

 variations of the current ; but the instrument seems more 

 especially appropriate to experiments on the cardiac action 

 current. 



Marey (37) was the first to use this instrument in determin- 

 ing the electrical phenomena concomitant with the cardiac systole. 

 He found that on leading off from the ventricle of the frog or 

 any other animal, the electrometer gave a single oscillation at 

 each systole. If the entire heart is connected with it, two 

 oscillations can be observed in the column of mercury. The one 

 is referred by Marey to the auricular, the other to the ventri- 



Fio. 129. Photographic record of cardiac action current, a, In the Frog's heart ; I, in the heart of 

 Tnrtoise. Time-marking in seconds. (Marey.) 



cular systole. Marey also succeeded in fixing these movements 

 by photographing the image of the mercury meniscus upon a 

 very sensitive plate moving at uniform speed. He concluded 

 from these experiments that there is at each systole only a 

 single variation of current (Fig. 129, a and b). Burdon- 

 Sanderson and Page employed this method as a means of con- 

 trolling and completing their rheotome experiments. There 

 appears to be a fundamental coincidence between the " theoretical " 

 curve (constructed from rheotome experiments) of the variations 

 in the frog's heart excited at one point of the ventricle, and that 

 projected on to sensitive paper by the mercury column of the 

 capillary electrometer. This appears directly from comparison 

 of the two Figs. 172, l>, and loO, a. It may be seen on the 



