POLARIS A TION AND EX C IT A TION. 559 



the intermolecular dissociation of oxygen which is the vera causa. 

 The hypothesis has been obviously framed to account for the exciting 

 efficiency of longitudinally-directed currents and the inadequacy of 

 cross-directed ones, and is by far the most satisfactory of all attempts 

 to give a picture of the molecular basis of an excitable tissue which 

 shall be in harmony with our modern knowledge. In spite of this, it 

 appears to the present writer to be inadequate, since it explains neither 

 the varying phenomena produced by temperature, nor the still more 

 subtle differences which justify the conclusion that the phenomena of 

 nerve conduction and of nerve excitation are to a great extent inde- 

 pendent of each other. The theory would probably need considerable 

 modification in order to embrace these. It has, however, the great 

 merit of accentuating the crux of the present position, namely, that 

 there is no definite standpoint except that which links excitation with 

 polarisation. The latest development of this view has been made 

 by Boruttau. He regards the electrical response of nerve as in 

 reality a catelectrotonic effect ; this necessitates the assumption that 

 polarisation and excitation are different aspects of the same state, 

 since catelectrotonus must be understood as the presence of those 

 electrolytic changes which are produced at the cathode of a polarising 

 current. 1 Hermann 2 has recently drawn attention to the circumstance 

 that in 1872 he framed a conception of the excitatory state in muscle 

 and nerve, based upon the following lines : — (1) Such tissue is excited 

 by the establishment of an adequate cathodic and the disappearance of 

 an adequate anodic polarisation (i.e., electrolytic change of a certain 

 type) ; (2) the excited tissue becomes at the seat of its excitation relat- 

 ively negative to those unexcited portions which are in the neighbour- 

 hood ; (3) cathodic polarisation is thus produced in the latter districts, 

 and on this attaining an adequate intensity, the state of excitation 

 occurs in such districts ; (4) this state of excitation must itself similarly 

 influence the neighbouring unexcited parts, and be thus successively 

 assumed by such parts (i.e., it is propagated). The fundamental distinc- 

 tion between the state of excitation and cathodic polarisation is that, 

 whereas the former may be propagated, the latter is not, but is estab- 

 lished simultaneously throughout the tissue in a diminishing quantity. 

 A certain intensity of cathodic change is necessary for the production 

 of the state of excitation, and this is only reached in the immediate 

 neighbourhood of the changed tissue ; the electrotonic decrement 

 which, in accordance with the laws of electrical distribution, is 

 present in every polarisable moist conductor, thus becomes an im- 

 portant factor in determining the production of a localised state of 

 excitation. 



In regard to the whole subject, it must be remembered that the 

 chemical changes which undoubtedly underlie vital activity must, like 

 all others of this nature, be resolved into the interaction of electrolytes. 

 Electrolysis, such as gives rise to the electromotive phenomena of 

 polarisation, is but one result of such interaction, and it is unquestion- 

 able that electrolytes may be present although no electrical indications 

 of their presence have been observed. Although, therefore, in our 

 present state of knowledge, the connection between exciting efficiency 



1 Boruttau, Arch. f. d. ges. Physiol., Bonn, 1894, Bd. lviii. S. 51 ; ibid., 1896. 

 Bd. lxiii. S. 154. 



2 Ibid., 1897, Bd. lxvii. S. 257 ; ibid., 1898, Bd. lxxi. S. 277-294. 



