72 INDUCTION SHOCKS 
well as by those of galvanic origin arise from the cath- 
ode,* and since the resistance of the physiological 
cathodes must be small in comparison with that of the 
whole mass of tissue traversed by the current, we are 
justified in considering tissue resistance as external to 
the actual seat of stimulation, and need make no dis- 
tinction between this and the other resistances that may 
be included in the secondary circuit. 
The Method of Experimentation. In studying the 
influence of secondary resistance experimentally the 
usual procedure has been to introduce known, non- 
inductive, resistances into the secondary circuit and to 
observe the effect of their introduction upon the stimu- 
lating value of the shocks sent through the circuit. As 
a check upon this method some experiments were per- 
formed in which different amounts of tissue were in- 
cluded between the stimulating electrodes, and thus the 
resistance of the tissue itself was varied. This latter 
method is of course less certain than the former, since 
the inclusion of more or less tissue in the circuit may mean 
a variation in the number and irritability of the physio- 
logical cathodes involved. 
Tissue resistances were determined by means of an 
ordinary Wheatstone bridge according to the Kohl- 
rausch method, with an alternating current to avoid 
* Chauveau: Journal de la physiologic, 1859, ii, pp. 490, 553. See 
also Biedermann: Elektrophysiologie, Jena, 1895, ii, p. 622. 
