8 CHANGES OF EXCITABILITY IN NERVES 



Of more weight than these investigations are those of Bilharz 

 and O. Nasse, of Munk, of Griinhagen, of Wundt, and of Hermann 

 and Bernstein, which have been conducted with all the care that 

 researches of this nature demand. They also confirm in all 

 essentials Pfliiger's results, but serve at the same time partly to 

 complete and partly to amend them, or to give a different theoretic 

 significance to the facts discovered by him. A short glance at 

 these will indicate their importance. 



Under the direction of du Bois-Reymond, Bilharz and O. Nasse 

 tested Pfliiger's laws with mechanical stimuli 1 . For this purpose 

 they availed themselves of Heidenhain's tetanomotor. The in- 

 crease or diminution of the tetanus produced by it, when a 

 constant current was passed in a given direction, served as a test 

 of the change of excitability which then occurred. 



Of course the test-stimulus injured the nerves to a very con- 

 siderable extent. The nerve was hammered for six seconds 

 continuously, and after each excitation got one to two minutes 

 to recruit ; yet in most cases it did not bear more than 6-8 

 successive stimulation experiments. So far as one can gather 

 from the brief descriptions of the authors, they passed the polar- 

 ising current in one direction only throughout each series of 

 experiments. 



With fresh nerves they established by this procedure the complete 

 correctness of Pfliiger's laws. As soon as the polarising current 

 was closed a diminution took place at the positive pole in the 

 tetanus elicited by the tetanomotor, at the negative pole an increase. 

 When the experiment was continued the reverse relation set in ; 

 first there was no change when the current was closed, and after 

 further application of the mechanical stimulus closing the current 

 yielded precisely the opposite result, namely at the positive pole a 

 strengthening, at the negative a weakening of the tetanus. The 

 authors obtained just the same result when they produced local injury 

 of the nerves with chemical substances. Afterwards Bilharz found 2 

 that other modes of injuring a nerve, for example the transmission 

 of a very strong constant current through it, or the bringing of a 

 red hot wire near it, &c. gave occasion to the same deviation from 

 Pfliiger's results. 



From the brief account which the authors have published of 

 individual experiments it is impossible to gather on what these 



1 Bilharz und 0. Nasse, Archiv fur Anatomie und Physiologic, 1862, pp. 66-83. 

 3 Bilharz, Archiv fur Anatomie und Physiologic, 1862, pp. 84-89. 



