22 THE CELL AS A PHYSICO-CHEMICAL UNIT 



involve changes in the pernieabiUty of the cell mem- 

 brane, reducing the ease with which the foreign sub- 

 stance is able to penetrate into the cytoplasm. 



The activity of antibodies may take two rather con- 

 spicuously different forms. The antibody may be re- 

 leased from the cell and combine with the foreign body 

 or foreign organism, before the latter reaches the cell. 

 Or alternatively the antibody may be present on the 

 outside of the cell membrane, and react with the foreign 

 body, to prevent its penetrating into the cell. 



Two rather obvious conclusions follow from some of 

 the arguments advanced above. The first is that, as the 

 result of secretory activity of the cell, to give the average 

 concentration of a drug in a cell is practically meaning- 

 less, since it is very improbable that any drug is uniform- 

 ly distributed through the cell as a whole. Secondly, 

 there is a competition between the build-up of a sub- 

 stance inside a cell, and the rate at which it is removed 

 by detoxication or other processes. Both these points 

 must receive proper consideration if the action of drugs 

 is to be fully understood. 



Self-reproducing Bodies 



One of the most characteristic activities of biological 

 systems is their ability to reproduce themselves. The 

 cellular bodies which we at present anticipate may be 

 able to do this, or know are able to do this, are nuclear 



