THE MUSCLE-NERVE PREPARATION 25 



effect. It is proper to use non-polarisable electrodes whenever a 

 galvanic current is led through a preparation. 



A simple form of galvanic element is furnished by two wires, one 

 of copper, the other of iron or zinc. If these are placed with one end 

 of each in contact with the moist nerve-muscle preparation, and if the 

 other ends are made to touch one another, the muscle will contract ; 

 as in Galvani's original experiment. 



Fleischl's rheonome is designed to show that not only the change of 

 potential but that the suddenness of the change is an important factor 

 in stimulating with a galvanic current. The rheonome consists of a 

 bridge composed of two curved pieces of zinc capable of being rotated 

 about a raised centre. One end of each piece has a terminal attached 



FIG. 30. Diagram of Fleischl's rheonome. 



to it (upper terminals) ; the other end which should be amalgamated 

 dips into saturated solution of zinc sulphate contained in a circular 

 groove in the wooden base of the instrument. Wires from a battery 

 are brought to opposite sides of the groove and come into connexion 

 with the zinc sulphate solution by amalgamated zinc terminals (lower 

 terminals). The upper terminals are brought into relation with a 

 muscle-nerve preparation by other wires, and when the battery circuit is 

 closed part of its current passes to the preparation, while part is short- 

 circuited through the zinc sulphate. The amount of short-circuiting 

 depends upon the position of the rotating bridge. Most current passes 

 through the preparation when the ends of the bridge are opposite the 

 lower or battery terminals. On now rotating the bridge this current 

 is diminished, and it vanishes when the rotation has attained 90 

 of the circle, gradually increasing again as this point is passed. If the 

 rotation is slow, there is no stimulation of the preparation, in spite 



