THE ELECTRICAL RESPONSE. 413 



that this mechanism is molecular, i.e., that the electromotive function 

 of muscular substance or of nerve substance is dependent on their 

 respective molecular structures. Although, therefore, du Bois-Keymond's 

 molecular theory, in the form given to it by its author, does not appear 

 to aid in the understanding of the relation between the mechanical, 

 chemical, and electrical processes which are concerned in the response 

 of a muscular element to stimulation, the recent development by 

 Bernstein of the chemical aspect of the theory appears to be of greater 

 value. 



Du Bois-Reymond's "molecules" were electromotive only. They were 

 of prismatic form, and were supposed to be arranged in series end to end, their 

 ends or poles being negative to their equators. Bernstein's molecules are also 

 prisms arranged in the same way, but their fundamental attribute is chemical, 

 that is, their poles are able to attach to themselves electro-negative groups 

 of atoms (oxidisable material), while their sides attach oxygen. This change, 

 which may be designated polarisation, is the first effect of excitation. It is 

 the immediate antecedent of the explosive oxidation of which the transforma- 

 tion of chemical into mechanical energy is the consequence. Any molecule 

 which is the seat of this change is able to communicate a similar state to the 

 molecules on either side, of which the poles face its poles ; and so we have the 

 propagation in two directions of the " excitatory wave." 



The chemical processes above described necessarily involve mechanical and 

 thermal consequences. At the moment of explosive oxidation, mechanical 

 stress takes the place of the chemical tension which is thereby relieved. This 

 mechanical stress is itself transformed into heat and external work, in 

 proportions which are dependent on the conditions set forth in the preceding 

 section. As regards the order in which these changes occur, Bernstein's 

 scheme is in accordance with views which have been already stated. 

 Chemical explosion comes first with its concomitant electrical manifesta- 

 tions, then follow the thermal and mechanical phenomena of muscular 

 contraction. 



Such is Bernstein's theory. It explains nothing, but it is of use as 

 enabling us to think of excitation, propagation, oxidation, electrical 

 change, mechanical stress, change of form, production of heat, as all 

 parts or manifestations of one and the same process. 



The simple statement already made, that in muscle and nerve, 

 relative capability of function (i.e. fitness for its performance) is indicated 

 by relative electrical positivity (that is to say, that of two parts of 

 identical function, in structural continuity with each other, the one which 

 is at the time most capable of performing that function is positive to 

 the other), springs out of experimental results independently of any 

 theory. In accordance with this statement, it will be shown in the next 

 paragraph that action is always attended by disappearance or diminution 

 of the capability of acting ; a part, in becoming active, becomes at the 

 same time relatively negative to other parts. 



Electromotive phenomena of muscle when excited. — The two 

 kinds of mechanical change which were studied in the first chapter — 

 the single response which follows an instantaneous stimulation and the 

 persistent one which is evoked by continuous stimulation — have their 

 counterparts in the electrical phenomena which we have now to examine. 

 The continuous electrical change which corresponds to tetanus has been 

 long known. It was recognised by Matteucci, and investigated by du 

 Bois-Eeymond, who bestowed on it the designation Negative Variation, 



