254 ELECTRO-PHYSIOLOGY CHAP. 



from the point of contact of the anode with the ureter, and 

 whether, on the other hand, there is local continuous contraction 

 at the kathode. The latter may indeed be ascertained by means 

 of the magnifying lens, so that it can hardly be doubted that 

 the polar excitation effects in the ureter in situ are manifesta- 

 tions analogous with the corresponding effects of excitation in 

 the intestine. 



The striking opposition between Engelmann's data, and the 

 results of experiments on the organ in situ, suggests that the 

 apparent reversal of polar effects depends essentially upon differ- 

 ences in the physical conditions, and in particular on the distribu- 

 tion of current. Experiments directed to this end have confirmed 

 the correctness of the assumption, and may also furnish the key 

 to the explanation of the manifestations which appear in many 

 other smooth muscular parts in the proximity of the anode, and 

 which we have previously referred to. Since the excised ureter 

 of mammals is still excitable after several hours, if warmed to 

 body-temperature, it is easy to experiment on it under different 

 conditions. If such a preparation is laid upon a glass plate, 

 warmed from below at 3840, and wetted with physiologica 

 salt solution, or better, with a small strip of moist filter-paper, the 

 consequences of excitation, when the electrodes are applied any- 

 where along the muscle, coincide in respect of localisation with 

 Engelmann's results from the ureter of the living animal. It 

 appears as clearly as can be desired, however the electrodes are 

 applied, that the ureter lying loosely upon its attachment con- 

 stricts at the kathode at the moment of closure, after which the 

 contraction progresses in undulations, or in one or the other direc- 

 tion. The same occurs at the anode with stronger currents, and 

 longer duration of closure, on opening the circuit. If the excised 

 ureter is then, without otherwise altering the conditions of ex- 

 periment, laid upon a thick pad made of layers of filter-paper, or 

 on a sufficiently heated block of salt clay, an. opposite reaction 

 will be exhibited with equal regularity, with both bipolar and 

 unipolar excitation, since, as in the fresh organ in situ, the make 

 excitation appears at the anode, the break excitation at the kathode. 

 It is clear that this can only be explained by differences in current- 

 distribution. If the thin muscular canal of the ureter is 

 stretched freely, or on a non-conducting support, the current will 

 be distributed somewhat according to Fig. 91 (after Engelmann). 



