in ELECTRICAL EXCITATION OF MUSCLE 279 



condition of increased excitability would spread from the kathodic 

 end over a certain larger or smaller area of the tract lying 

 between the poles. At first sight this seems to correspond with 

 the observation that when loth electrodes are so applied to the 

 lower end of the muscle that one (kathode) is 2 to 3, mm. 

 away from the tendon end, and the other about 4 mm. higher,, 

 the height of the minimal twitch discharged by the closure of a 

 descending induction current, during polarisation by a very weak 

 descending battery current, is greater than it was before. Closer 

 examination, however, shows that this conclusion is not justified, 

 the experimental result being due solely to the structure of the 

 muscle. Since, i.e. the muscle-fibres are not all of the same 

 length, and are inserted at the lower end into an oblique surface, 

 the physiological kathode of the muscle traversed longitudinally 

 in a downward direction, must necessarily extend over a measur- 

 able and tolerably extensive portion of the lower half of the 

 muscle. So long therefore as, under the experimental conditions 

 described above, a sufficient number of ends of fibres fall under 

 the kathode of the test current, a perceptible alteration of excita- 

 tion effects during polarisation manifesting itself either as 

 increase or as diminution of excitability is perfectly intelligible. 

 The latter, i.e. apparent extension of depression of excitability 

 over the intrapolar muscle region may be observed under the 

 same experimental conditions, either when with descending 

 polarising and test currents the intensity of the former increases, 

 or when with an ascending polarisation current the exciting 

 electrodes, which are close together, are brought so near to the 

 lower end of the muscle that the excitation is still in part dis- 

 charged within the anodic area. If, however, the test electrodes 

 are pushed farther and farther along the muscle to its upper 

 end, it may easily be ascertained that with the given strength 

 of the polarising battery current a perceptible change in the 

 height of twitch before and during the passage of current cannot 

 be demonstrated at any other point of the intrapolar area. It 

 is therefore solely the spatial distribution of the points of 

 entrance or exit of current at the lower end of the muscle, due 

 to irregularities of structure in the sartorius, which occasionally 

 produce a wider diffusion of the excitatory changes confined, 

 as we shall see, to the physiological anode and kathode. If 

 the negative test electrode lies outside the region of the physio- 



