ACTIONS ON ENZYMES III 



narcotics upon respiration is that of Quastel upon the 

 respiration of the brain tissue. Table xxi shows some 

 of his results. Inspection of this Table indicates that 

 with the substances he was investigating a difference of 

 one double bond in structure was sufficient to cause 

 profound modification of narcotic activity, and an 

 equally profound modification in the ability to inhibit 

 oxygen uptake by brain tissue. It is clear that the very 

 small difference in partition coefficient produced by a 

 difference in structure of one double bond could not 

 possibly account for the differences of activity of these 

 different molecules. One therefore wonders whether this 

 is an instance in which a specific structure of the mole- 

 cule producing narcosis is important, and whether this 

 structure is not specific for one of the enzyme systems 

 involved in respiration. 



Some doubt however is thrown upon this by the 

 results given in Table xxii. This shows in one column the 

 concentration of narcotic which is necessary to produce 

 a given degree of narcosis in the rat, and in the other 

 column, the degree to which the uptake of oxygen by 

 brain tissue is inhibited by the narcotic concentration. 

 If all the narcotics are acting in the same manner, one 

 would except them to inhibit the respiration of brain 

 by the same amount when present in equi-narcotic con- 

 centrations. But, in fact, urethan produces only one- 

 fifth of the inhibition produced by an equi-narcotic con- 

 centration of avertin. The evidence, therefore, is not very 



