6 INDUCTION SHOCKS 
and also upon the rate of their movement; the more rapid 
the change in the field, the higher the intensity. 
The method used in physiology for bringing about 
alterations of the field within the secondary coil is to 
make and break the current through the primary. 
FIG. 2. Schema of induction apparatus (Lombard), h repre- 
sents the galvanic battery connected by wires to the primary coil A. 
On the course of one of these wires is a key, k, to make and break the 
current. B shows the principle of the secondary coil and the connec- 
tion of its two ends with the nerve of a nerve-muscle preparation. 
When the battery current is closed or made in A, a brief current of high 
intensity is induced in B. This is known as the making or closing 
shock. When the battery current is broken in A, a second brief induc- 
tion current is aroused in B. This is known as the breaking or opening 
shock. 
When the primary current is made there is a sudden in- 
crease in the lines of force cutting the secondary coil; 
when the primary current is broken these lines of force 
suddenly disappear. The currents induced by the make 
and the break of the primary circuit are obviously of 
