326 ELECTRO-PHYSIOLOGY CHAP. 



between them (28, p. 52). The "molecular tension," i.e. the 

 potential force inherent in each molecule, which "accumulates 

 persistently in the process of nutrition," is identified by Bernstein 

 with the electrical E.M.F. of du Bois-Reymond's peripolar mole- 

 cules, as neutralised in excitation, with correlative movements of 

 the molecules. " The tendency in the latter to neutralise their 

 electrical E.M.F. is opposed by an inhibitory force (unknown to 

 us in its intrinsic nature), which prevents any movement of the 

 molecules in the resting state " (Pfliiger's " molecular inhibition "). 

 Whether this is the result of friction, of elasticity, or of both is 

 uncertain ; there is a play of forces " which tends to maintain 

 the components of the molecules (i.e. the peripolar molecules 

 formed of two dipolar bodies) in their natural position, and re- 

 stores them to the same after each alteration." Any stimulus, 

 of whatever kind, " disturbs the natural position of the molecules," 

 whereby molecular inhibition is interrupted, and there is neutral- 

 isation of the electric potential. As regards electrical excitation 

 in particular. Bernstein accounts for the reinforcement of mole- 

 cular inhibition at the positive pole, and consequent decreased 

 mobility of the molecules (diminished excitability), as well as the 

 lowered inhibition and raised mobility (increased excitability) at 

 the negative pole, by the attraction or repulsion exerted by the 

 polarising electrodes upon the peripheral molecules next to them. 

 The positive electrode fixes these, as it were, in their place, the 

 negative zones being turned towards the pole, while the kathode, 

 by repulsion of the same zone, renders them more mobile. This is 

 why, at closure of the current, excitation proceeds from the kathode 

 only. The molecules at the positive pole remain in their normal 

 position ; " at the negative pole, on the other hand, inhibition is 

 weakened, the exciting energy preponderates and causes excita- 

 tion." On opening the circuit, inhibition falls suddenly at the 

 positive pole, and the increased potential energy of the molecules 

 is now discharged, and induces excitation. Electrotonic altera- 

 tions of excitability, and other phenomena, receive a similar 

 interpretation. 



The dictum long since expressed by du Bois-Eeymond 

 (Untersuchungen, II. i. p. 387), to the effect that yalciniir 

 excitation is nothing more tlian the first stage of electrolysis in 

 excitable tissues, may still (though in a somewhat different 

 sense) be accepted as the most apt theoretical definition of the 



