STRENGTHS OF FARADIC STIMULI 19 
the nerve alone. By placing in the circuit beyond the 
shunt another resistance equal to one-half that of the 
nerve the total resistance of the secondary circuit is 
made equal to what it would be if the shunt and the 
added resistance were both removed. Since, however, 
the nerve is in a divided circuit, both branches of which 
have equal resistance, it receives only one-half the cur- 
rent generated in the secondary coil. That secondary 
position at which the nerve receives threshold stimula- 
tion when in the divided circuit is determined, and then 
'Nerve, of Res. W 
/ 
~w~^ 
FIG. 4. Diagram showing method of inserting resistances in the 
Wertheim-Salomonson method of calibration. After Gasten. 
the shunt and the additional resistance are cut out. 
Now the nerve receives the whole current from the sec- 
ondary instead of half of it, and if the secondary posi- 
tion is found at which the threshold stimulus is again 
imparted we know that this second current has just 
half the stimulating value of the first. We have thus a 
method for comparing stimuli, which admits of exten- 
sion sufficient for the complete calibration of a coil. 
It has, however, the shortcoming, already noted for 
Kronecker's method, of giving values applicable only 
