THEORY OF THE BREAK-CONTRACTION. 53 



i be explained by the susceptibility of the nerve to internal 

 polarisation, without making the slightest attempt to show how all 

 the phenomena characterising and attending the break-contraction 

 could be deduced from it 1 . 



Moreover, the internal polarisability of nerves had not been studied 

 sufficiently to admit of a true parallel being drawn between it and 

 the break-contraction. It is easy to explain, therefore, why this 

 statement has received no further attention from physiologists. 



Then came Pfliiger's investigations, which have to so great an ex- 

 tent impressed the nerve physiology of to-day. Pfliiger's conception 

 of the break-contraction has since then been accepted almost without 

 objection, although, as already explained, it supplies no explanation 

 of the phenomena, but only an elegant statement of their laws. 



A remarkable theory was put forward about the same time by 

 Chauveau. According to him the physiological action of electricity 

 is 'the result of a mechanical disturbance communicated to the 

 molecules placed in the path of the current V 



The constant current in general excites only by means of 'an 

 accessory instantaneous current of high tension, with which it 

 commences ; ' and similarly by means of ' an accessory instantaneous 

 current of high tension, with which it terminates 3 .' Of these 

 currents the first flows in the same direction as the stimulation- 

 current, and the second in the opposite direction. The action of 

 the last is assisted by the polarisation-current 4 . 



In later times, so far as I know, only H. Munk has attempted to 

 advance a real theory of the break-contraction. His theoretical 

 view starts from the phenomenon of Porret, and is thus presented 

 by the author himself : * The excitation of the nerve is due in the 

 first place to the direct displacement of the nerve fluid in the 

 direction of the current, and similarly, by the return of the fluid, 

 when the current is opened, to those parts of the nerve whence it 

 had come. Inasmuch as these movements of the nerve-fluid extend 

 over the extrapolar tract to the muscle, the muscular contraction is 

 produced by the motion of the nerve-fluid independently of its 

 direction provided that the motion is propagated to the muscle 

 with sufficient intensity and velocity 5 / 



Munk therefore would regard both the make- and the break- 

 contraction as caused by a mechanical excitation. It is, however, 



1 Matteucci, Comptes Kendus, torn. 65, 1867. 



2 Chauveau, Journal de la Physiologic, iii. No. ix. p. 5 2 > January, 1860. 



3 Ibid. loc. cit. pp. 6 1-66. * Ibid. loc. cit. p. 70. 

 5 H. Munk, Archiv fur Anatomic, Physiologie, &c., 1866, p. 383. 



