248 ELECTRO-PHYSIOLOGY CHAP. 



at this point, under some conditions. That, notwithstanding, a 

 frequently well-marked total contraction of the muscle bundle 

 should almost invariably occur with unipolar anodic excitation, 

 is because the fundamental excitation at closure of the current 

 does not proceed from the anode itself, but originates in the 

 region proximal to it, as will presently be described. This 

 accounts for the somewhat surprising fact that closure of current 

 at the anode, in electrical excitation of the worm's integument, 

 produces a (sometimes maximal) constriction of the segment in 

 direct contact, and also accounts for the marked shortening of 

 Echinus and Holothurian muscles in unipolar anodic excitation, as 

 well as the no less striking rupture of the former at the spot 

 at which current enters. 



From this point of view it is easy to explain the excitation 

 effects in the intestine of invertebrates (31) at first sight 

 so unexpected and irregular. If a given surface -point of a 

 quiescent loop of the small intestine of any mammal is brought 

 into contact with the anodic electrode, at sufficient intensity of 

 current, while the kathode is again applied to any indifferent part 

 of the body (liver, stomach, etc.), a circular constriction is formed, 

 as in worms, and may, under some conditions, lead to the 

 complete closing up of the intestinal tube at the point in question. 

 This contraction persists throughout the duration of closure, pro- 

 vided the latter does not extend over too long a period, and 

 equalises itself again without much delay when the current is 

 broken. This effect of excitation can be very well seen in loops 

 of the intestine that are moderately extended by fluids or gases. 

 Provided the exposed intestine is not unduly cooled, and is still 

 highly excitable, there will at closure of the current, in addition 

 to the local contraction of the circular muscles at' the anode, be a 

 more or less evident peristaltic, or anti-peristaltic, movement in 

 the proximity of the point directly excited, of which in this case 

 it is hardly possible to say whether it is directly caused by a 

 branch of the current, or is carried on from the primary seat of 

 excitation. We shall see later that under certain conditions the 

 anode does actually become the point of departure of peristaltic 

 contractions spreading on either side, while in other cases a 

 merely local constriction appears. Various sections of the 

 intestine in this respect give a uniform reaction, and at most 

 show differences in degree, which are due to the unequal develop- 



