THE MEASUREMENT OF BREAK SHOCKS 
33 
lutely instantaneous, the initial rise would be instan- 
taneous likewise and the secondary current would begin 
with its maximum value. Since, however, there is al- 
ways, even under most favorable conditions, a certain 
amount of sparking at 
the contacts, there is 
never an instantaneous 
break, and the initial 
rise is constantly 
present. Helmholtz * . ..__. 
demonstrated, with the FlG I0 Curve mustra ting the course 
aid of. an ingenious ap- of a break induced current after 
paratus, that the phys- Fleming ' 
iological effect of a break induced current is chiefly 
exerted by that part embraced within the ascending limb 
of the curve. By breaking the secondary current at 
various points in its course he found that the physiolog- 
ical effect was virtually as great when the current was 
broken at the moment of reaching its maximum intensity 
as when it was allowed to run its entire course. Recent 
investigations carried out by means of short galvanic 
currents have shown, it is true, that the stimulating 
effectiveness of a shock is to some extent dependent as 
well upon the descending portion of the curve,t so that 
* Helmholtz: Loc. cit., S. 537. 
t Gildemeister: Pfliiger's Archiv filr die gesammte Physiologic, 
cxxxi, 1910, S. 199. 
