36 ACTIONS OF DRUGS ON SURFACES 



sorbed must present an organisation of ionising groups, 

 polar groups and non-polar groups as specific as that 

 which is to be found in the drug itself. If this criterion 

 is fulfilled the possible energy of adsorption is large. 

 But a group in the wrong position, or having the wrong 

 orientation, may readily prevent the dove-tailing of the 

 drug and the surface and thus prevent many of the sites 

 of potential adsorption becoming effective. Thus the 

 presence of a methyl group in the wrong place may read- 

 ily reduce the ease of adsorption of a drug by several 

 thousand calories, and cause it to be relatively inert. 

 This theory may be regarded as a plausible one. It is 

 very difficult to establish such theory. 



Mechanism of Lysis 



One of the aspects of drugs which has often attracted 

 attention is the ability of certain substances to cause cy- 

 tolysis. Cytolysis usually involves a direct action upon 

 the plasma membrane of the cell. When lytic substances 

 are considered from the point of view of surface ch em- 

 istry it is seen that they are likely to produce their action 

 partly by the formation of complexes with the mole- 

 cules constituting the cell membrane, and partly by dis- 

 solving in the lipoid layer of the plasma membrane. As is 

 indicated in Table ii, some of these substances probably 

 react primarily with proteins to form complexes, some 

 react primarily with lipoids and some react with both. 



