312 THE OUTGO OF ENERGY 



secured to the lever. Thus the muscle, though 

 below the lever, will pull it upwards when con- 

 traction takes place. Let the two writing points 

 be in the same vertical line. Start the drum at 

 rapid speed. Two curves will be recorded : one 

 by the contraction of the ventricle, the other by 

 the rheoscopic muscle, stimulated to contract by 

 the action current. The contraction of the rheo- 

 scopic muscle will slightly precede the contraction 

 of the ventricle. 



Current of Action of Human Heart. Place 

 normal saline solution in two beakers. In each 

 let the foot of a n on-polar izable electrode dip. 

 Connect the electrodes through the usual short- 

 circuiting key with the electrometer. Bring the 

 meniscus into the field. Let an assistant place a 

 finger of each hand in the saline solution. 



When the short-circuiting key is opened the 

 meniscus will be displaced by the skin (secretion) 

 current. Careful observation will show also a 

 periodic variation synchronous with the .systole 

 of the heart. 



The diphasic character of the action current of 

 the heart, shown so well by the capillary elec- 

 trometer to the unaided eye, appears even more 

 clearly when the movements of the meniscus are 

 recorded by projecting them on a quickly moving 

 photographic plate. By photography, too, the di- 



