104 ACTIONS OF NARCOTICS 



series are studied there is also a close parallel between the 

 reduction of surface tension and the narcotic effect. 



However there are three main criticisms which must 

 be levied against this rather simple theory. These are: 



1. The parallel between surface tension reduction and 

 narcotic activity may be misleading. The reason for 

 this is that in a homologous series the relative reduc- 

 tion in surface tension obtained with different mem- 

 bers of the series is merely a reflection of the differ- 

 ences in the hydrocarbon moiety ofthe molecule. There 

 are many other physico-chemical properties of mole- 

 cules which also are a reflection of the hydrocarbon 

 content of the molecule. For example, changes in the 

 oil-water partition coefficient run closely parallel to 

 changes in surface tension, for the simple reason that 

 both properties closely follow the hydrocarbon content 

 ofthe molecule. Thus from the studies of narcosis, one 

 is justified in concluding that there is a close parallel 

 between the narcotic effect and the amount of hydro- 

 carbon in the molecule. But one is not justified in 

 concluding that any particular individual physico- 

 chemical property which runs parallel to the hydro- 

 carbon content is necessarily the one through which 

 the physiological effect is mediated. 



2. Even if the effect of narcotic substances is exercised at 

 an interface, studies on the air-water interface may 

 very well be irrelevant. The important interfaces of a 

 cell are oil-water, protein-water, nucleic acid-water. 



