92 ELEMENTARY PHYSIOLOGY. [iX. 



2. Single Induction Shocks. 



Now connect a Daniell's cell with the top screws 

 of the primary coil interposing a key to break 

 the current, connect the electrodes with the 

 secondary coil of a Du Bois Reymond's in- 

 duction machine^, place the marker of the se- 

 condary coil at 10 on the scale, and, the frog's 

 leg being at rest, shut and open the key several 

 times. 



At each shutting and opening of the key, i. e. at 

 each momentary induced current, a single sharp 

 movement of the leg will take place. The ' single 

 induction shock' causes a single contraction or 

 spasm of the muscles of the leg. If the nerve 

 slips off the electrodes during the movements, 

 be careful not to pinch it in replacing it. 

 If good contractions are not obtained with the 

 secondary coil at 10, push it up gradually over 

 the primary coil, one division at a time. 



3. Shut and open the key as rapidly as you can, 

 'for a few seconds. The contraction of the muscle 

 taking longer time to develop than the induced 

 current, each contraction will take place before 

 the preceding has disappeared, and the leg will 

 remain rigidly contracted, or nearly so, as long- 

 as the breaking and making of the primary cur- 

 rent is kept up. In other words, tetanus is pro- 

 duced. This is however more easily brought 

 about as follows. 



1 Cp. Appendix, 



