304 THE SO-CALLED SECONDARY ELECTROMOTIVE 



For the present sufficient material has been obtained to determine 

 the correctness of my explanation of du Bois-Reymond's observa- 

 tions. 



The phenomena of the extrapolar-currents, to the investigation of 

 which we now turn, will render the decision of the point much 

 more certain. 



4. Investigation of extrapolar after-currents in Nerves 

 and Muscles. 



The extrapolar after-currents, following the passage of a current 

 through a given portion of tissue, have been hitherto only inves- 

 tigated in the case of nerve. Fick was the first to observe that 

 on either side of the polarising-current there appeared an after- 

 current opposed to it in direction 1 . Shortly afterwards I entered 

 on the same enquiry 2 and found that the two extrapolar regions 

 were completely different in their behaviour ; on the side of the 

 anode I found, like Fick, an after-current opposed in direction to 

 the previous current, on that of the kathode, however, an after- 

 current, similar in direction to the previous current ; the former 

 was much more marked than the latter. On repeating his experi- 

 ments Fick obtained results similar to mine 3 . Du Bois-Reymond 

 mentions these phenomena, but does not state whether he has ever 

 experimented upon the subject or not. 



Since the publication of the work I did at that time, I have often 

 had the opportunity of observing again the extrapolar after-currents 

 of nerve, especially in the years 1871, 1872, when I was investigat- 

 ing the extrapolar after-currents in the case of platinum wires 

 surrounded by fluid 4 . The new work of du Bois-Reymond and the 

 explanation which, I believed, should be given to his supposed ' posi- 

 tive polarisation,' prompted me to a systematic re-investigation. As 

 a matter of fact, the old experiments could not be considered as 

 exhaustive, since in these the multiplier was used, the sluggish 

 needle of which would not answer to a rather rapid change of 

 current-direction ; moreover, du Bois-Reymond's results encouraged 

 making experiments with high strengths of current (which were 



1 ' Centralblatt f. d. med. Wissensch.' 1867, p. 436. 



2 ' TJntersuchungen zur Physiologic der Muskeln und Nerven,' Part 3, p. 71. 

 Berlin, 1868, 



3 ' Untersuchungen aus dem physiol. Labor, d. ZuricherHochschule/ Part I, p. 129. 

 "Vienna, 1869. 



4 Pfliiger's ' Archiv,' vol. v. p. 267 ; vol. vi. p. 318. 



