EXCITATION AND CONDUCTION 63 



in the actual determination of carbon dioxide were 

 reproduced. 



From the results so obtained the minimum concen- 

 tration which produced a reversible loss of irritability was 

 chosen for our experiments on the carbon dioxide pro- 

 duction, and we are thus assured that the nerve has been 

 narcotized, but that, since its excitability returns, no 

 permanent injury has been caused. The carbon dioxide 

 production of the nerve thus treated has been determined 

 and compared with that of a normal nerve. These 

 results are tabulated with the physiological data and 

 given in Table VII. 



ETHYL URETHANE 



As shown by physiological tests, a freshly isolated 

 claw nerve on immersion in a 4 per cent solution of ethyl 

 urethane loses its excitability within ten minutes. Such 

 a nerve, however, if left in a moist chamber for ten or 

 fifteen minutes and then returned to sea-water, comes 

 back to a normal condition of excitability with appar- 

 ently no injurious effects. That the nerve so narcotized 

 gives off less carbon dioxide than a normal one can be 

 demonstrated qualitatively as follows : 



Two nerves of approximately the same weight are 

 isolated, and one is immersed in sea-water while the 

 other is treated with a 4 per cent urethane solution for 

 ten minutes. At the end of this time their rates of 

 carbon dioxide production are compared simultaneously 

 in the biometer by placing the normal nerve, for example, 

 in the right chamber and the other in the left. Within 

 ten minutes the difference in carbon dioxide output 

 will become evident, for not only does the precipitate 



