INTRODUCTION 



47 



cient drug action the rate at which a drug penetrates into 

 a cell must be large compared with the rate of detox- 

 ication. Commonly drugs must also pass other membranes 

 in addition to those of cells, such as the complex mem- 

 branes composing the intestinal epithelium, the cuticle 

 of a parasite etc. It is thus clear that there is much point 



Concentration of Ag* 



Fig. II. The action of Ag on the invertion of sugar, (a) Inhibition of 

 purified invertase; (b) inhibition of invertion by yeast cells; (c) amount 



of Ag taken up by yeast cells 



in knowing how changes in the physical structure of a 

 drug may modify its ability to permeate various types of 

 membrane. 



Even when we are studying the effect of drugs upon 

 simple cell suspensions, such as those of bacteria and 

 yeasts, the action may prove to be much more compli- 

 ated than when we are dealing with those homogenates 

 which are dear to the biochemists. Fig. ii shows the 



