ACTIONS UPON SURFACES 



103 



ity increases. The effect shows up in sonie cases rather 

 clearly when the surface tension is studied of solutions 

 of substances, all of which have roughly the same narcotic 

 activity. There is a strong tendency for the solutions 

 of equi-narcotic activity to have the same surface tension. 

 Figure 19 shows an example of the parallel between 



10 



Concenfrafion 



Fig. 19. TTie action of ethyl urethane in reducing the respiratory reflex in 

 the cat (•) and in reducing the tension at the air-water interface ( X ) 



reduction in the surface tension at the air-water inter- 

 face and reduction in a reflex of the cat. Traube there- 

 fore proposed that the narcotic substances exercise their 

 effects primarily on surfaces, and that the effect is due 

 to the reduction of surface tension. The strength of his 

 case rested upon the fact that when a given substance 

 is studied at different concentrations there is a parallel 

 between narcotic activity and reduction in surface ten- 

 sion. And when different members of a homologous 



