BY DR. MICHAEL FOSTER. 389 



position that the induction shock given becomes the mini- 

 mum stimulus required to produce a muscular contraction, 

 that is, any further removal of the secondary from the pri- 

 mary coil will lead to the absence of all contractions. This 

 minimum stimulus then giving, in the absence of the polarizing 

 current, a slight but obvious contraction, send an ascending 

 polarizing current through the nerve; the contraction will be 

 wholly absent. Remove the polarizing current, and excite 

 again ; the contraction will again make its appearance. 



Obs. V. Remove the secondary coil a little further away 

 from the primarj*, so that an induction shock gives no con- 

 traction where the polarizing current is cut off from the nerve. 

 Pass a descending current through the polarizing pair, i. e., 

 throw the portion of nerve in which the exciting pair rest 

 into katelectrolonus. Again pass the same induction shock as 

 before: a contraction will follow. 



Shut off the polarizing current, and after waiting a few 

 minutes, send the induction shock through the exciting pair a 

 third time. No contraction, or at best a very slight one, will 

 be obtained. 



Ihu-iny the passage of a constant current, the irritability ix 

 increased in the region of katelectrotonus. 



()I>*. VI. The other arrangements being the same, put the 

 magnetic interruptor into connection with the primary coil. 

 Record the movements of the lever on the revolving cylinder. 



With a not very strong interrupted current, throw the mus- 

 cle into tetanus, and as soon as tetanus is established, send 

 an ascending current through the polarizing electrodes for a 

 few seconds only, and afterwards close the key of the inter- 

 rupted current. 



The curve of the tetanus on the recording cylinder will ex- 

 hibit a marked fall (down even to zero if the polarizing current 

 be strong enough) at the moment when the polarizing current 

 breaks into the nerve, and a corresponding rise when the 

 polarizing current is shut off. 



This is simply another way of showing the diminution of 

 irritability in anelectrotoi.us. 



Obit. VII. Repeat the observation, using a very weak teta- 

 nizing current, and let the polarizing current be descending. 

 The making of the polarizing urrent will be marked by a rise, 

 and the breaking by a corr< .ponding fall in the tetanus curve, 

 indicating, as before, an increase of irritability in katelectro- 

 tonus. 



Obs. VIII. Ligature the nerve between the two pair of elec- 

 trodes, and repeat all the observations. The polarizing current 

 will have no effect at all upon the results of the exciting < i ur- 

 rcnt. Otherwise, part of the effects described above will have 



