ESSENTIALS OF PHYSIOLOGY. 



observed, in slowly contracting muscles, such as the cardiac muscle 

 of the frog. 



Electrical Changes in Muscle. When a constant current is passed 

 into a muscle through metallic electrodes, electrolysis takes place in 

 the muscle; the electrolytes accumulate .near the electrodes, and give 

 rise to a current which passes in the opposite direction to that in 

 which the constant current is passing, and tends to neutralise the 

 latter. This phenomenon is known as polarisation, and in recording 

 the electrical currents occurring in muscle it is necessary to use non- 

 polarisable electrodes. 



The electrical currents in muscle may be observed .by means of 

 either the capillary electrometer or the string galvanometer. The 



N 



LJ 



\ 



ARC 

 LAMP 



CAMERA 



FIG. 3. Scheme of string galvanometer. 



a, b is the quartz thread ; N and S are the electro-magnets ; E is a microscope. 

 The magnified image falls on the slit H, and is photographed. (Hume.) 



capillary electrometer consists of a glass tube drawn out at one end 

 to a capillary, and partly filled with mercury; the capillary tube 

 opens into another tube containing 10 per cent, sulphuric acid. Two 

 platinum wires pass, One into the sulphuric acid, the other into the 

 mercury. When the electrometer is connected with two points of 

 different potential, the mercury moves up or down the capillary tube. 

 If the point connected with the acid is negative as compared with that 

 connected with the mercury, the latter moves down towards the acid ; 

 if the point connected with the acid is positive, the mercury moves 

 away from the acid. The movements are rapid and are proportional 

 to the difference of potential' "between the two points under observation ; 

 they may be directly observed under the microscope, or may be recorded 

 photographically. 



The string galvanometer consists of a very delicate quartz thread, 

 silvered over and hanging between two strong electro-magnets through 

 which a current is passing ; by means of terminals passing from each 

 end of it, the thread can be connected with a muscle or other structure. 



