888 STIMULATION OF NERVES. 



Further, it is evident from the different results of breaking 

 and making, that the entrance into katelectrotonus and ane- 

 lectrotonus has not the same relation to the origin of a nervous 

 impulse as lias the exit from those states. 



Lastly, from the different behavior of the ascending and 

 descending currents, it appears that the effect of the entrance 

 into katelectrotonus is not the same as that of the entrance 

 into anelectrotonus, and that the effects of the exits from these 

 states likewise differ. 



III. Electrotonus as affecting Irritability. Arrange 

 a nerve-muscle preparation in the moist chamber, with lever. 

 etc. Prepare two pair of non-polarizable electrodes. Place the 

 end of the nerve on one pair, about 1 or 2 cm. apart ; connect 

 this, the. polnrizimj pair, with a battery of one or two cells, 

 the commutator intervening. Place the second pair between 

 the first pair and the muscle, and connect this, the exciting- 

 pair, with an induction coil. 



When the polarizing current is made a descending one, the 

 portion of the nerve on which the exciting electrodes rest, will 

 lie in the n-gion of katelectrotonus ; when ascending, in nnflrr- 

 trotonus, 



O/AS-. III. The polarizing current being shut off (the handle 

 of the commutator horizontal), pass a single induction (open- 

 ing) shock through the " exciting" pair, and record the con- 

 traction. Shift the secondary coil, if necessary, until a con- 

 traction of moderate excursion is obtained, and note the dis- 

 tance of the secondary coil from the primary. 



Now let the polarizing current (i.^re/nl in the nerve (through 

 the polarizing pair of electrodes) ; the exciting pair will ac- 

 cordinglv now be in the region of anelectrotonwt, 



;ect the cont ract ion which may be caused by the making 

 (and subsequent breaking) of the constant polarizing current ; 

 and while the current is thus passing in an ascending direc- 

 tion, send a single induction shock of the same strength as 

 before through the exciting pair, and record the contraction. 



Shut ot!' the polarizing current, and after a few minutes 1 

 rest, send a third time the same induction shock through the 

 exciting pair. 



Of the three contractions thus called forth by the same 

 stimulus (the induction shock) under different circumstances, 

 it "ill be found that the second is much smaller than the first, 

 but the third nearly of the same size (it may be larger) as the 

 first 



/>nrii:ij tin' jifi.^nt/c tif ti <-n*t<ni/ current, the irritability of 



n iii-ri'f /s I (.<.' in-il in the anelectrotonic region. tJie tunncxtimu- 

 lu* giving r/Vv (<> a */<<//; ncrrutix /m//f//.<'. (ind xu to a smoller' 

 contraction. 



I V. Shift the secondary coil until it reaches such a 



