150 ELECTRO-PHYSIOLOGY CHAP. 



mediate product of the battery, for how could this engender them, 

 seeing that it is no longer present ? The organism which has 

 been in circuit must yield them itself, and can only yield them 

 because it has been in the circuit, since otherwise it would not 

 have done so." 



It would, as Pflliger remarks, be hard to find a more correct 

 description of the peculiarities of the opening excitation ; and the 

 recent attempts at giving another interpretation of this original 

 theory of the break excitation (by which it depends upon the dis- 

 appearance of a' peculiar state engendered by the current) can only 

 partially be endorsed. 



The later observations of Pfliiger and others state that: as 

 the closure excitation is caused by the appearance of katelectro- 

 tonus (i.e. the sum of alterations in the nervous substance 

 produced at the kathode by current), so the opening excita- 

 tion is the immediate consequence of the disappearance of the 

 anelectrotonic changes. The alterations of excitability which 

 accompany electrotonus, or its disappearance, seem however to 

 authorise a further step in the explanation of these phenomena. 

 It must always be remembered that (as has been repeatedly 

 expressed from other points of view) no sharp dividing-line 

 between increase of excitability and excitation can be predicated. 

 Eise of excitability beyond a certain point may pass directly 

 into excitation, while, on the other hand, a weak persistent latent 

 excitation, which has not produced any visible consequences, may 

 only be expressed in a heightened capacity for response. Both 

 appearance of katelectrotonus and disappearance of anelectrotonus 

 are accompanied by a marked and easily demonstrated increase 

 of excitability, which reaches its greatest intensity at the poles, 

 and in fact discharges an effective excitation there, provided other 

 conditions are favourable. From this point of view the altera- 

 tions of excitability in nerve as well as in muscle (which are 

 only the partial manifestation of electrotonus) fall into immediate 

 relation with the excitatory phenomena characteristic of the two 

 moments of appearance and disappearance, closure and opening 

 of the current. There is no special alteration of the living- 

 matter fundamental to excitation, and distinct in nature from 

 the alterations expressed in rise of excitability, but both together 

 are different manifestations of one and the same change of state 

 which the excitable substance suffers under the influence of 



