SYNTHETICAL DRUGS 581 



hydrogen atoms of the benzene nucleus also greatly increases 

 the germicidal efficacy of phenol and the cresols. Tetrabromo- 

 para-cresol (XXVI.) and tetrabromo-ortho-cresol are among 

 the most powerful of known germicides. 



It has generally been found that the introduction of the 

 acidic groups, carboxyl, CO a H, and sulphonyl, S0 3 H, diminishes 

 very markedly the toxic action of a drug. Benzoic acid, 

 C 6 H 5 .C0 2 H, for example, is a substance producing only a 

 very slight physiological effect. When a carboxyl group is 

 introduced into the phenol molecule in a position contiguous 

 to the hydroxyl group salicylic acid (XXVII.) is obtained. This 

 product, in the form of its sodium salt, is a very important 

 drug ; it has a powerful antiseptic and germicidal effect, is 

 free from the caustic property exhibited by phenol, and it 

 has, moreover, a specific action in acute rheumatism. In its 

 internal effect it greatly resembles quinine, even to the extent 

 of producing a ringing in the ears and transient deafness. 

 When there is toleration of the drug the exhibition of salicylic 

 acid gives excellent results in the treatment of rheumatic 

 troubles, but in certain cases the acid is apt to produce gastric 

 disturbances, and to overcome this unpleasant effect various 

 derivatives of salicylic acid have been put forward. 



The well-known drug aspirin, acetylsalicylic acid (XXVIII.), 

 is a good example of this series. 



O.CO.CH3 OH OH 



^CO.H /^NCO.-.CgH, ^Nco.,.c (1 h 4 .nh.co.ch 3 



XXVIII. XXIX. XXX. 



Owing to its insolubility in the gastric juice it is devoid of 

 the irritating action of salicylates on the stomach, but it is 

 decomposed by the alkaline intestinal juices setting free salicylic 

 acid. In order, however, that its action may be entirely 

 beneficial it is important to bear in mind that alkalis of any 

 kind should not be administered immediately after aspirin. A 

 weak acid, such as citric acid, is, on the other hand, a useful 

 adjuvant. 



The salols are also employed to avoid the ill effects of 

 salicylic acid on the stomach. They pass through this organ 

 unchanged, and are then decomposed by the alkalis of the 

 intestine. In these circumstances salol itself (XXIX.) is then 



