themotherapy 

 Table 12 



141 



It will be seen that the effective drug concentration 

 is inversely proportional to the degree of ionisation and 

 that the amount of ^^-aminobenzoic acid required for 

 inhibition of the drug is very nearly proportional to the 

 amount of drug in the ionised state. ^j-Aminobenzoic 

 acid is completely ionised at ]:>H 7. Its ion may be 

 represented as at A in Fig. 5. 



2-3 A 2-4 A 



A B 



Fig. 5 



The electrons belonging to the sulphur atom of a sul- 

 phonamide (C in Fig. 5) are attracted by the oxygen 



