THE PHENOMENA OF CONDUCTION IN NERVE 



141 



A B 



These results have led to the early belief that nerve-tissue' cannot 

 be fatigued and that the nerve impulse is a physical phenomenon. 

 It should be remembered, however, that these deductions have been 

 based upon experiments which were made in a medium of air and under 

 conditions greatly favoring the activity of nerve. Contrary to the 

 view just expressed, Bayer and Frohlich have shown that the refrac- 

 tory period of nerve may be considerably lengthened by means of 

 narcotics or by displacing the air by an inert gas, such as hydrogen or 

 nitrogen. It was also noticed that the power of conduction of nerve 

 is markedly diminished in a medium of 

 this kind and remains so until the nerve 

 has again been transferred into an atmos- 

 phere containing oxygen. Thorner^ has 

 modified this experiment by placing the 

 nerves of two nerve-muscle preparations 

 in a chamber containing nitrogen (Fig. 

 83). One of these nerves was then sub- 

 jected to a tetanizing current centrally 

 to this chamber (A). By measuring the 

 amplitude of the wave of negativity it 

 was found that the excitability and con- 

 ductivity decreased very rapidly in the 

 tetanized nerve, but a similar, although 

 much slighter, effect was also detected in 

 the inactive nerve (B). Further evidence 

 in favor of the view that nerves may be 

 fatigued, has more recently been pre- 

 sented by Garten. 2 While testing differ- 

 ent non-medullated nerves, it was noted 

 that the action currents sweeping over 

 the olfactorius of the pike, ceased very Fig. 83.— Fatigue of Nebve. 

 shortly after the beginning of its tetaniza- ^ ^nd B two nerves placed 



.• J Tj J. r-L j.T_ in glass chamber. The latter is 



tion and did not reappear even after the connected through c with gas 

 electrodes had been applied to some other generator, s points of stimuia- 

 part of this nerve. This fact tends to *i«^: ^' galvanometers placed 



, ,i,,i /.,• /. • upon nerves to test their irrita- 



snow that the fatigue of nerve is never biiity. 

 restricted to the segment stimulated but 



involves this structure in its entirety. Very similar results have 

 been obtained by Burian^ in the non-medullated nerves of cephalo- 

 pods. This investigator, moreover, has proved that these symptoms 

 of fatigue are not dependent upon electrotonic alterations in the area 

 stimulated. In summing up, it may be stated that the difficulties 

 formerly encountered in proving fatigue in nerve must be assigned 



1 Zeitschr. fur allg. Physiol., viii, 1908, 530. 



2 Beitrage zur Physiol, der markl. Nerven, Jena, 1903; also see: Snowton, Proc. 

 R. Soc, Ixvi, 1900, 379. 



^ Intern. Kongress der Physiol., Heidelberg, 1907; 



