DEFENCE MECHANISMS 21 



processes involve the addition to the molecule of a polar 

 residue, such as glucuronic acid or sulphuric acid. As a 

 result of this type of procedure, the chemical and physi- 

 co-chemical character of the foreign substance may be 

 altered so as to make it comparatively innocuous. Thus 

 menthol in the body is largely converted into menthol 

 glucuronide, which is devoid of toxic properties and 

 also has much less surface activity than has menthol it- 

 self. Also the increase in polarity greatly reduces the 

 probability that the detoxicated molecules will re-enter 

 the cell once expelled after detoxication. 



An alternative method of detoxication is frequently 

 encountered in the form of destructive reactions, in 

 which the foreign molecule is broken down into smaller 

 and less toxic compounds. These processes are usually 

 enzymic. Thus toxic amines are often detoxicated by 

 amine oxidases. 



Amongst the longer term processes which may develop 

 on the physico-chemical level, there are included in- 

 creased efficiency in detoxication of a given foreign sub- 

 stance, the development of ''resistance" to the foreign 

 substance, and the development of antibodies. 



The development of resistance probably takes many 

 forms. It may consist of an increase in ability to detoxi- 

 cate or to destroy a foreign body. This type of resistance 

 bears many formal semblances to the development of 

 adaptive enzymes in bacteria and yeasts. There is also 

 some evidence that the development of resistance may 



