ANESTHESIA 187 



of 2.5%, which was probably due, either wholly or in 

 part, to the fact that the resistance of the sea water was 

 greater than that of the mixture from which the ether 

 had partly evaporated. During the next 400 minutes 

 no rise occurred. The results are shown in Fig. 81. 



This outcome is very significant, for it shows that 

 the increase of permeability produced by ether is not 

 reversible, while, as we have seen, the decrease of 

 permeability is easily reversed. Since the essential 

 characteristic of an anesthetic is the reversibility of its 

 action, we must conclude that anesthesia is associated 

 with the reversible decrease of permeability and not with 

 the irreversible increase of permeability. 



In view of the importance of this result the experi- 

 ment was repeated many times, the fall of resistance 

 (before placing in sea water) varying from 6 to 25%, but 

 always with practically the same result. On placing in 

 sea water there were sometimes irregular fluctuations 

 (amounting to 5% or less) but no recovery. 



This result is the more strildng inasmuch as material 

 of which the resistance has fallen as much as 5 to 10% in 

 NaCl recovers completely when placed in sea water, 

 and may even undergo this treatment daily for several 

 days in succession without injury.^ 



The fall of resistance below the normal may be taken 

 as a measure of the toxicity. The toxicity increases with 

 the concentration, and it should be noted that it is greatly 

 decreased if the material is allowed to stand in an open 

 dish, owing to the evaporation of the ether. If the 

 material be placed in a closed jar, oxygen must be sup- 

 plied. The other alternative, frequent renewal of the 

 solution, is usually preferable. 



" See page 82. 



