224 



IRRITABILITY 



rior root is then stimulated, tetanus is also produced but of some- 

 what shorter duration. If, while obtaining tetanus reflexly by 

 stimulation of the ninth root, a faradic current of short duration 

 and not too weak is applied to the tenth root, then a summation 

 of excitation occurs, an increase in the reflex contraction. 

 (Figure 57, A and B.) When, on the other hand, the tenth root 



B 



Fig. 57. 



Summation of two excitations in the spinal cord produced by stimulation of the ninth and 

 tenth posterior root Lower line indicates faradic stimulation of the tenth, upper line 

 of the ninth root. 



