CONDUCTIVITY 119 



only primarily for the reason that we intend especially to analyze 

 the conductivity of excitation on this occasion, but also because 

 no other effects of stimulation except those of excitation can be 

 conducted from the part affected by the stimulus to the sur- 

 roundings. 



Although considered on theoretical grounds it appears more 

 or less improbable that depression is extended from the place of 

 its origin, it is very easy to convince one's self experimentally of 

 the fact that depression follow^ing a stimulus is invariably local- 

 ized to that portion directly affected by the stimulus. The nerve 

 furnishes a very favorable object for this purpose. If a nerve 

 muscle preparation of the frog is made and introduced in the 

 glass chamber previously described containing platinum elec- 

 trodes, and another pair is applied to the nerve between the cham- 

 ber and the muscle, it is possible to subject the stretch of nerve in 

 the chamber to various agents, producing a paralyzing effect. In 

 this way it may be exposed to an atmosphere of pure nitrogen 

 for example, or to narcosis as by ether, chloroform, carbon diox- 

 ide and other gases, to an increase in temperature or to other 

 agents, without these in any way affecting the irritability of the 

 nerve stretch situated over the electrode between the chamber 

 and the muscle. The contractions of the muscle, which are pro- 

 duced by stimulation of the periphery region of the nerve with 

 stimuli of a definite strength, remain unaltered, even when the 

 asphyxiated stretch of nerve in the chamber is already completely 

 degenerated. The central depression of a ganglion cell of a 

 motory neuron is likewise wholly without influence on the degree 

 of excitability of its nerve fiber, as I was able to demonstrate^ 

 in the reflex inhibition of the motor neurons of the spinal cord 

 of the dog. (Figure 14.) That which is conducted by the 

 nerves is solely the process of excitation. 



It is our task to analyze in detail the conditions involved in the 

 conduction of excitation in order to obtain a deeper insight into 

 the physics of this process. A comparative survey of a series of 

 various types of living substance shows us that they differ in 



1 Max Verworn : "Zur Physiologic der nervosen Hemmungserscheinungen." Arch. f. 

 Anat. u. Physiol, physiol. Abt. Suppl. 1900. 



