NERVE 



59 



How do you know it is not a summation in excitation? 



At the end of the experiment, if time permits, the prepara- 

 tions may be replaced in salt solution and the conductivity of 

 the nerves restored. 



FIG. 16A. 



The experiment may then be repeated, exchanging the 

 position of the two preparations so as to be sure that the result 

 is not due to inequalities in them. 



