284 ELECTRO-PHYSIOLOGY CHAP. 



nounced decrease in height of twitch could be observed in the latter 

 case, under uniform conditions. It is, moreover, unmistakable 

 that the excitability of the preparation just before polarisation 

 commences, determines the time in which the diminution of ex- 

 citability occurs after closure of the constant current. As a rule 

 it may be said that depression follows the period of heightened 

 response, in the kathoclic fibre points of a weakly-polarised muscle, 

 the more quickly in proportion as the excitability of the muscle 

 is ab initio lowered from any cause, local or general. 



This is exhibited as well in preparations taken from frogs 

 with deficient vitality, as in those in which excitability is only 

 locally diminished (at the kathode) by the temporary passage of 

 current. The latter effect can also be seen in Table II. of the 

 experimental series. Within 34 sees, after closure of the weak 

 polarising current the augmentative effect of the homodromous 

 make induction current used as test excitation at first strongly 

 marked became practically zero. So soon after break of the 

 constant current as the muscle had recovered itself sufficiently 

 to yield distinct twitches with the same test as before the first 

 passage of current, the polarising current was closed again. The 

 height of twitch immediately reached the same proportions as in 

 the first series ; on the other hand, the excitability of the 

 kathodic points of fibres diminished much more quickly than 

 before, since a passage of current of 20 sees, suffices to inhibit 

 the effect of the same stimulus. The depression and final in- 

 hibition of previously augmented excitation caused by a homo- 

 dromous induction current, makes its appearance more or less 

 quickly in proportion with the intensity of the battery current 

 sent through the muscle. 



Starting from minimal polarising currents, gradually increased 

 in intensity by pushing up the rheochord slider, and giving the 

 muscle time to recover itself between each pair of experiments, 

 it is easy to verify the accuracy of this last statement. At a 

 certain intensity of current, varying in proportion with the 

 excitability of the preparation, the increase of kathodic response 

 only occurs plainly at the moment immediately consequent on 

 closure, and is hardly perceptible with further augmentation of 

 current intensity. This does not, however, as might be concluded 

 from the foregoing observations of Engelmann on the rabbit's 

 ureter, occur for the first time when the constant current lias 



