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CHAPTER VIII. 



ELECTROTONUS. 



THE qualities of a nerve are found to be altered by 

 the passage through it of a current of electricity. To 

 the altered state of the nerve Du Bois-Reymond ap- 

 plied the term ELECTROTONUS, first used by Faraday 

 to denote the molecular disturbance produced in a 

 wire subject to induction. One of the most important 

 changes is in the nerve's excitability. The subject is 

 one of extreme difficulty, and at the same time of 



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great interest ; and in this chapter some of the ex- 

 periments connected with the subject will be given in 

 detail, in the hope that they may enable the student 

 more easily to pursue in other works the theoretical 

 portion of the subject. 



The rheocord (pe'os = a stream ; xP^ = a cord). 

 -The effects produced by the electrotonic state of a 

 nerve depend to a considerable extent on the strength of 

 the constant current used to produce the condition ; 

 and, consequently, some apparatus is required by means 

 of which the current strength may be varied at pleasure 

 and with rapidity. Such an apparatus is the rheocord 

 of Da Bois-Reymond (Fig. 42). It is formed of a 

 block of wood, near one end of which there runs a 

 transverse plate of ebonite, the shaded portion of the 

 figure. On this plate of ebonite are seven brass 

 plates (white in the figure), separated from one 

 another by a space. Each of these plates has a semi- 

 circular piece cut out of each side. The semicircular 

 gap of two opposing plates forms a round hole, into 

 which a brass plug, with an ebonite top, can be in- 

 serted to form a metallic connection between the 



