250 ELECTRO-PHYSIOLOGY CHAP. 



arrangement of the muscular layers presenting unmistakable 

 analogies with the relations described in Holothuria. In neither 

 case do the external longitudinal muscles of the intestine present 

 a coherent layer ; they are either exclusively (holothurian), or pre- 

 dominantly (large intestine), compressed into single band-like stria? 

 (t&enite), between which the circular muscles are visible. If an 

 electrical current leaves the muscle at any point of such a tsenia, 

 an obvious, localised, persistent contraction appears, which is 

 absent when the current enters at the same spot ; then, on 

 the contrary, there is usually segmental constriction of the wall 

 of the intestine, due to excitation of the circular muscles. If the 

 anode happens to fall 011 any part of the surface of a saccule, 

 the last-named consequences of excitation occur only the more 

 plainly. If, on the contrary, the current leaves by the surface of 

 a saccule, a small, scar-like swelling will appear (running at 

 right angles with the direction of the fibres), which remains 

 localised to the immediate proximity of the kathode, and as 

 may be recognised with artificial enlargement is essentially 

 caused by a local persistent contraction of the circular muscle- 

 fibres only. This appearance is throughout analogous with the 

 small, sharply-defined transverse swelling of Holothurian circular 

 muscles apparent on kathodic excitation. This local kathodic 

 excitation of the circular muscles of the intestine is less visible, 

 for obvious reasons, in all cases where a longitudinal muscular 

 layer of considerable thickness is present. Yet the peculiar 

 dinted constriction of the upper surface of the small intestine, 

 from the centre of which the scar-like swelling arises, must be 

 referred partly to the local kathodic excitation of the circular 

 muscles covered by the longitudinal fibres. So too, the tendinous 

 origin of a tamia of the large intestine appears with kathodic 

 excitation to be concerned in the production of a local circular 

 muscle swelling. If the peculiar and characteristic reaction 

 of the circular muscles of Holothuria on anodic excitation, as well 

 as the corresponding excitation effects in the muscular integu- 

 ment of worms, is remembered, there can hardly be a doubt that 

 the circular, or segmental, constriction of the intestinal wall at the 

 anode is due to the same causes. The relations are not indeed 

 as clear and easily recognised as in the former case, and least so 

 in the small intestine. The well-filled colon of Herbivores seems 

 much more appropriate to these manifestations. Here, with weak 



