ELECTRO-PHYSIOLOGY. 589 



deviates. By noting the deflection of the needle, it is found that the 

 longitudinal surface of the muscle is positive and the transverse 

 section is negative. The deflection of the needle is caused by the 

 current of injury by the transverse section of the muscle. It is 

 called the demarcation current, because the difference of potential 

 appears at the demarcation between the dying and the injured mus- 

 cle. The injured part of the muscle is negative to the uninjured 

 part and the current in the galvanometer is from the longitudinal 

 (positive) surface to the uninjured negative transverse surface. 



Capillary Electrometer. This instrument is an electrical mano- 

 meter and shows electrical pressure. It consists mainly of a glas* 



Fig. 224. Diagram of Capillary Electrometer. (STABLING.) 



Hg., Mercury. The two terminals are represented as leading off two points 

 at the base and apex of a frog's heart, a b. 



tube ending in a fine point, which is partly filled with clean mercury 

 and then placed in communication with a pressure apparatus. The 

 capillary end of the glass tube dips into a tube containing mercury 

 and a 20-per-cent. solution of sulphuric acid. Into the tube with 

 sulphuric acid is fused a platinum wire which forms one connection 

 with the lower column of mercury. Another platinum wire is con- 

 nected with the capillary tube. Anything which alters the surface 

 tension will cause the mercury to move. If now two unpolarizable 

 electrodes are connected with a capillary electrometer with a short- 

 circuiting key, and the center of a muscle is laid on one of the non- 

 polarizable electrodes and the divided transverse end on another non- 

 larizable electrode, then when the mercury meniscus is watched 



