PRACTICAL PHYSIOLOGY 



47 



effect upon the conducting power of .the nerve. 

 Remove the CO 2 by a current of air, and repeat 

 the observation. 



Another experiment may subsequently be made 

 with ether vapour instead of CO 2 . 



Electrotonic effects of constant current on 

 nerve excitability. Make a pair of non-polari- 

 sable electrodes by plugging one end of each of two 

 short glass tubes with modelling clay moistened 

 with normal saline solution, filling the tubes with 



FIG. 30. EFFECT OF CARBON DIOXIDE ON CONDUCTION IN NERVE. 



saturated solution of zinc sulphate, and placing in 

 this solution an amalgamated zinc wire (Figs. 7, 8). 

 To these electrodes is led the current of a galvanic 

 battery consisting of at least two cells (Fig. 31). 

 Insert a rheochord, a mercury key, and a commuta- 

 tor into this circuit {polarising circuit) ; by means 

 of these the polarising current can be varied in 

 strength and in direction, or can be cut off or put 

 in at will. Another circuit (exciting circuit) must 

 also be put up, and must include an induction coil 

 with a mercury key in the primary circuit ; the 



