70 INDUCTION SHOCKS 
placed on the levers at the points where the ringers press 
upon them, and upon the handle by which the rod, , is 
rotated. 
In addition to its applicability for both make and 
break shocks this key has the advantage of preserving 
uniformity of action for a long time with little attention. 
In this respect it is superior even to platinum contact 
keys, which, as is well known, suffer from oxidation 
after prolonged use. There is no doubt, however, that 
well made automatic platinum-contact keys, properly 
looked after, give break shocks of sufficient uniformity 
for the general purposes of the physiologist. 
