230 ELECTRO-PHYSIOLOGY CHAP. 



preparation, provided it is so arranged that the cut surface is 

 perpendicular to the direction of current. 



For the sake of brevity, we may, with Hermann, denote the 

 direction of the exciting current which lies towards the cut 

 surface " atterminal " (" admortal "), the other as " aUerminal " 

 (" abmortal "). The reaction observed may then be shortly 

 expressed as follows : Immediately after injury to the cardiac 

 apex, the closure of atterminal currents is ineffective, while under 

 similar conditions the closure of dbterminal currents is excitatory. 

 Obviously we have here a complete analogy to the response of 

 the sartorius of which one end has been injured (or otherwise 

 chemically altered), and the same conclusions may be deduced in 

 both cases. In the first place, experiment proves convincingly that 

 the contractions of the heart with electrical excitation proceed 

 exclusively from the spot where the current passes from the living 

 muscular tissue into the foreign medium beyond it, whether this is 

 salt solution or dead muscle-substance. This represents the^>7/.s/<v- 

 logieal Imilwdc of the preparation, and here alone can the make 

 excitation originate. On this presumption only does the effect 

 of local injury upon excitability to closure of atterminal currents, 

 with failure of effect upon excitability to abterminal closure, 

 become intelligible. It holds good, however, for the apex of the 

 heart, which consists of innumerable irregularly fused cells, just 

 as much as for the approximately parallel -fibred monomerous 

 sartorius. 



In both cases the excitation propagates itself at closure over 

 the whole surface of the muscle, from its point of departure, by 

 conductivity (from cell to cell), the exact seat of the kathode on 

 the surface of the preparation seeming to be quite indifferent, 

 while the excitability of the points affected has, on the other 

 hand, an important influence on the consequences of excitation. 

 If the current leaves by an injured point, excitation takes place 

 at a less excitable spot, and the effects can be interpreted just 

 as in sartorius, under similar conditions. The only noticeable 

 difference is the rapid restoration of normal reactions. Engel- 

 mann explains this naturally by the assumption that the single 

 cells, though connected by relations of conductivity with their 

 neighbours while living, die singly, each to itself ; in other words, 

 the process of dying does not pass over from cell to cell like 

 that of excitation. Where the superficial cells are quite dead. 



