58 PRACTICAL PHYSIOLOGY 



are examined and measured in exactly the same 

 way as those of muscle. 



Excitation current of heart muscle. Con- 

 nect the non-polarisable electrodes of the electro- 

 meter with a beating frog-heart, which may either 

 be removed from the body and laid with the 



Galvanometer. . - 



FIG. 39. ARRANGEMENT FOR EXAMINING MUSCLE CURRENT BY GALVANOMETER. 



base of the ventricle upon one electrode and the 

 apex on the other, or left in situ and the elec- 

 trodes connected with apex and base of ventricle 

 by thick threads wetted with salt solution. Each 

 contraction of the ventricle is accompanied by a to 

 and fro movement of the mercury meniscus of the 

 electrometer, the direction of which may be noted 

 and the alterations in electrical potential of base 

 and apex deduced therefrom. 1 



1 An accurate record of changes in electrical potential can be ob- 

 tained by photographing the excursions of the mercury meniscus. 



