262 ELECTRO-PHYSIOLOGY CHAP. 



Engelmaim showed that every little muscle -bridge which 

 unites two otherwise separate parts of the frog's ventricle, effects 

 a physiological process of conductivity between them, inasmuch 

 as the excitation coining from the auricle is carried through the 

 bridges to the lower portion of the ventricle. There is thus a 

 conductivity of excitation from cell to cell without any inter- 

 position of nervous elements. Similarly it may be shown that 

 the anodic wave of relaxation is propagated from one half of the 

 ventricle to the other, if any minute portion of the normal mus- 

 cular wall remains to establish connection. By carefully pinching 

 the side of an anodically relaxed ventricle of a large snail's heart 

 with small forceps, it is easy to make the greater part of its wall 

 in the middle section incapable of conducting. When subse- 

 quently traversed by current, relaxation can be seen to pass over 

 the small conducting bridges, although far more slowly than under 

 normal conditions. 



A contusion extending right over the middle part of the 

 ventricle, and dividing it into two excitable halves separated 

 by a small, unexcitable zone, affords a means of investigating 

 the phenomena which appear on excitation with the constant 

 current more exactly than is possible in the entire uninjured 

 heart. The experiment, indeed, presents certain difficulties, since, 

 owing to the great sensibility of the preparation to mechanical 

 excitation, the two halves of the ventricle are not seldom un- 

 equal in their capacity for response, one or other of them remain- 

 ing more distinctly contracted, or, at all events, not returning 

 to the relaxed state ; but notwithstanding this, a little practice 

 will generally obtain the desired result provided the animals are 

 large enough. If such a preparation is traversed by a battery 

 current of sufficient strength, we see as is to be expected that 

 only the anodic half relaxes, while the kathodic either exhibits 

 no changes, or contracts distinctly on closure of the current if its 

 tonus is but little apparent. On opening the circuit this reaction 

 is exactly reversed in favourable instances ; the kathodic section 

 of the ventricle relaxes, while the anodic goes into contraction. 

 It should be noted that both halves of the ventricle have their 

 physiological anode and kathode. That, notwithstanding this, an 

 effect can be detected upon one side only, is necessarily due to 

 the "fact that the density of current is less, on the one hand, at 

 the point of injury (owing to the larger section), while, on the 



