140 IRRITABILITY 



cannot be further increased. But above all, there is a series of 

 facts, which have been gained in the Gottingen laboratory, which 

 demonstrate apparently without doubt the validity of the "all 

 or none law" for the medullated nerve. These observations I 

 wish now to consider in greater detail. 



If a nerve of a nerve muscle preparation is drawn through a 

 specially devised glass chamber so that the middle portion can 

 be narcotized or asphyxiated and the nerve so arranged that it 

 rests upon a pair of electrodes in the chamber and upon a second 

 pair without the chamber and centrally located, then the nerve 

 can be narcotized or asphyxiated and thereby the alterations in 

 the irritability as well as the conductivity can be followed. In 

 order to obtain as distinct a picture of this alteration as possible, 

 I tested continuously the threshold of stimulation, which just pro- 

 duced minimal contraction in the muscle, and Frohlich 1 continued 

 these observations. As a result the following very remark- 

 able conditions were observed. During the increase of the depth 

 of narcosis or asphyxia the irritability sinks more and more with 

 regularity. The conductivity remains unaltered for a long time, 

 as the strength of the threshold stimulus is not changed until 

 irritability has fallen to a definite point. When this is reached, 

 conductivity disappears. (Figure 24.) The most important point 

 in this connection, however, is, that the conductivity disappears 

 simultaneously and practically momentarily for the excitation 

 produced by both weak and strong stimuli. When the stimula- 

 tion at the electrode placed centrally to the chamber does not 

 bring about response for threshold stimuli, maximal stimuli at 

 the same time also become inoperative. This is a very interesting 

 point, the importance of which has not until now been recognized. 

 This fact is not in harmony with the view held until now, that in 

 the nerve fiber different strengths of stimuli bring about excita- 

 tion of different intensity, and are then conducted. Let us now 

 clearly comprehend this problem. 



We have already seen that the wave of excitation meets with 

 a decrement of its intensity in the narcotized stretch, which 



1 Frohlich : "Erregbarkeit und Leitfahigkeit des Nerven." Zeitschr. f. allgem. Physi- 

 ologic, Bd. Ill, 1904. 



