ADVANCED EXPERIMENTAL PHYSIOLOGY 



317 



k b 



which is subjected to the change of temperature (Fig. 195). A 

 minimal stimulus is obtained for the nerve when the temperature is 

 that of the room, 15 C. The height of the contraction is recorded on a 

 stationary drum, which can be moved by hand before the next contrac- 

 tion. A current of cold water, 5 C., is passed through the tube ; the 

 stimulus will now produce a maximal contraction. Warming the nerve 

 will have an opposite effect. If, however, the experiment be per- 

 formed with fl , ( 

 very short 

 stimuli, such 

 as are pro- 

 duced in an 

 induction- 

 apparatus 

 with the 

 core remov- 

 ed from the 



primary coil, it will be found that cooling the point of excitation 

 diminishes the excitability. 



A similar degree of cooling has no effect upon the conductivity of 

 the frog's sciatic nerve. This can be readily shown by stimulation of 

 a portion of the nerve central to the cooled area. 



FIG. 195. Diagram of the experiment to show the effect of temperature 

 upon the excitability of nerve. 



CHAPTER XIII. 



THE INFLUENCE OF CARBON DIOXIDE, ETHER AND CHLOROFORM 



UPON NERVE. 



THE effects of the above agents upon the excitability and conductivity 

 of nerve can be shown by the following experiment. The sciatic nerve 

 of a muscle- and nerve-preparation is passed through two notches in 

 the cork of a small gas-chamber, 1 the holes are closed around the nerve 

 by kaolin moistened with normal tap-water saline solution, and the 

 top is closed by a glass cover-slip fastened down with kaolin (Fig. 196). 

 In this way the action of the gas or vapour is confined to one portion 

 of the nerve. The preparation is placed in a moist chamber after two 

 pairs of electrodes (a) and (b) have been arranged in the way shown in 

 the diagram. By means of glass tubes connected with long pieces of 

 rubber tubing the gas or vapour can be conducted through the gas- 



1 A small gas-chamber can be easily made out of a large^cork. With a large 

 borer the centre is cut out and a slice of the plug so removed is reinserted to form 

 the floor. Two needles are pushed through the walls of the chamber to form the 

 pair of electrodes (b). 



