k. 



280 ELECTRO-PHYSIOLOGY CHAP. 



observation (curve Jcjc^). In regard to excitability, Pniiger 

 (I.e. p. 349) determined a brief increase immediately after 

 closure of the polarising current. It is clear, as was pointed 

 out above, that the comparatively slow process of electro- 

 tonic alterations at any 

 given point of the nerve, 

 as well as the rapid diminu- 

 tion of intensity with in- 



P \^ creasing distance from the 



polarised part, must present 

 great obstacles to an experi- 

 v mental determination of the 



FIG. L'1-J. 



rate of transmission. Gal- 



vanometric time-measurements more particularly break down (as 

 Hermann pointed out, 35, p. 453) in this department, owing to our 

 ignorance of the time-distribution of the initial stages of electro- 

 tonus. Even the foregoing experiments of Bernstein cannot 

 therefore be regarded as decisive in this question of the trans- 

 mission of the electrotonic state, the more so since they are 

 opposed by other experiments which have not yet been contra- 

 dicted. Valerius von Baranowsky and Carl Garre* worked out 

 a series of experiments under Hermann's direction upon the rate 

 of diffusion of anelectrotonic alterations of excitability, partly on 

 Griinhagen's principle as described above, and partly by a method 

 of Hermann. A strong ascending current is led into the central 

 end of a nerve connected with its muscle, while (with a Helm- 

 holtz's switch) another weaker constant current, also in an 

 ascending direction, is closed as a test stimulus. Then, after 

 ascertaining that the polarising current per se gives only opening 

 and no closure twitches, while the weaker test current infallibly 

 excites at closure, and on comparing the magnitude of this closing 

 twitch with and without simultaneous closure of the polarising 

 current, it will be found that in the last case, even where the 

 two tracts of nerve are at a long distance from each other, 

 the test stimulus will be ineffective, or will discharge a weaker 

 make twitch than before. The fact that the interval between 

 the closure of the two currents was in these experiments some- 

 thing under O'OOOl sec., wives a value for the diffusion of 



O O 



anelectrotonus, which at a distance of 16 '5 mm. between the 

 two tracts of nerve is in any case greater than 10,000 x 16 '5, 



