EFFECT OF MICELLE FORMATION 4I 



micelles, the concentration of single molecules may be 

 independent of the total concentration, increases in con- 

 centration resulting merely in formation of more mi- 

 celles. The transition of micelles into single molecules of 

 solute may have a very high temperature coefficient. 

 Consequently the action of such a drug may also have 

 a very high temperature coefficient. 



2. If the activity of a homologous series of drugs is 

 plotted against the number of carbons in the molecule, 

 it is frequently found that somewhere in the region of 

 nine carbon atoms a maximum of activity is reached. As 

 the number of carbons in a series is increased, so also the 

 ease of adsorption of the molecule increases, and conse- 

 quently its activity per molecule rises. But as the num- 

 ber of carbons increases, so does the ease of formation 

 of micelles, and it commonly happens with drugs con- 

 taining an aliphatic carbon chain that the ease of forma- 

 tion of micelles increases more rapidly than the surface 

 activity increases. Thus a point is reached at which mi- 

 celle formation occurs before a concentration of the drug 

 as single molecules is reached at which its physiological 

 activity can become manifest. Hence the maximum in 

 the curve of activity plotted against number of carbons 



(Fig. 9)- 



3. If a second substance is present, which can form 

 micelles, a drug may be inactivated by combination with 

 the micelles. This is illustrated by Fig. lo. In this dia- 

 gram the rate of penetration of hexyl resorcinol into 



