THE PHENOMENA OF CONDUCTION IN NERVE 



139 



iTJp[n||n 



71 



lutely necessary for the proper function of this tissue. These experi- 

 ments consisted essentially in enclosing the nerve of a nerve-muscle 

 preparation in a small glass receptacle so that it could easily be sub- 

 jected to the influence of an inert gas, such as hydrogen or nitrogen 

 (Fig. 82). While the effect was never very striking, it could never- 

 theless be shown that the irritability and conductivity of the nerve 

 (N) decreased very markedly if kept in this inert medium for a period 

 of several hours. Moreover, the subsequent displacement of the inert 

 gas by oxygen was followed within a few minutes by a 

 complete restoration of the function of the nerve. This 

 proves that oxygen is one of the prerequisites of nerve 

 metabolism. As far as the production of acid is con- 

 cerned, no positive results have been obtained. In this 

 regard nerves differ very materially from the gray 

 matter of the central nervous system, because the latter 

 has been shown to become decidedly acid as a result of 

 activity.^ 



The fact that nerve tissue undergoes assimilative 

 and dissimilative changes, is also betrayed by the high 

 value of the temperature coefficient of conduction. It 

 has previously been mentioned that the speed of the 

 nerve-impulse is greatest in warm-blooded animals 

 and that even moderate rises in temperature give rise 

 to a much greater rapidity of conduction. In this re- 

 gard nerve-tissue behaves in accordance with the van't 

 Hoff law for chemical reactions. In addition, it should 

 be mentioned that nerve possesses a very appreciable 

 refractory period during which it cannot respond to 

 stimuli. In the case of the sciatic nerve of the frog j^^ ^^^^^ ^^ 

 this period amounts to 0.002 second, but may be in- nerve' muscle 

 creased by cold, asphyxia, anesthetics and narcotics. 

 It appears, therefore, that nerve-tissue requires a cer- 

 tain time for its anabolic changes and hence, if a 

 second stimulus is brought to bear upon it before it 



Fig. 82.— 

 Fatigue of 

 Nerve. 



preparation 

 drawn through 

 glass chamber. 

 The latter is con- 

 nected with Kipp 



has had sufficient time to complete these processes, it The stimulus is 

 must necessarily fail to conduct the succeeding impulse, applied at S. 



The brevity of the refractory period of nerve sug- 

 gests that its power of assimilation is unusually great, but this is 

 rather to be expected, because the conduction in nerve does not re- 

 quire a considerable expenditure of energy so that the compensation 

 for the preceding dissimilation can easily be effected without profound 

 chemical changes. This deduction is in complete harmony with the 

 structural peculiarities of nerve. Contrary to the gray matter of the 

 central nervous system, the white matter, as well as the peripheral 

 nerves, possesses a scanty and ill-defined network of blood capillaries 

 and lymph channels. This implies that the blood supply of this 

 1 Funke, Arch, fur Anat. und Physiol., 1859, 835. 



