THE INFLUENCE OF SECONDARY RESISTANCE 79 
R and R f respectively, have equal physiological effect. 
Since dissimilar inductoria fail to give corresponding 
values of Z at all secondary resistances, the value of A 
determined by this formula from one inductorium will 
not necessarily agree with its value as obtained from 
another. The value of A, therefore, does not depend 
solely upon the surface of the physiological cathodes, 
but in part also upon the construction of the inducto- 
rium. 
This variation in the values of A determined from dis- 
similar inductoria, which might lead one to question the 
validity o the equation in which A is employed, i.e., 
ZA 
|8 = > serves in fact to confirm strongly the valid- 
j\. -p A 
ity of that equation and the use of the expression to 
signify the specific value of the stimulus. This con- 
firmation rests upon the repeated observation that when 
equal stimuli are generated by dissimilar inductoria the 
values of are equal even though the observed values of 
Z and the computed values of A may be quite divergent. 
An experiment illustrating this point is summarized in 
Table VII. Details of the construction of the induc- 
toria used are given in Table VIII. The experiment 
shows that dissimilar inductoria give for equal break 
stimuli perfectly concordant values if all the factors 
which make up the final expression for stimulation 
strength are taken into account. 
