CHEMOTHERAPY 147 



nucleotide) or by nicotinamide. Sulphanilamide, sulpha- 

 thiazole, and sulphapyridine all inhibit the growth of 

 Sonne's bacillus, and this effect, but not the respiratory 

 inhibition, is reversed by ^^-aminobenzoic acid. Sulpha- 

 thiazole is said to have a similar inhibitory effect on 

 CO -enzyme or nicotinamide stimulated metabolism. The 

 explanation may be that sulphathiazole and sulpha- 

 pjrridine are isosteric and accordingly could replace one 

 another in adsorption on the co -enzyme or that sulpha- 

 thiazole may act on a different part of the metabolism 

 chain, involving decarboxylation (see p. 43). The primary 

 action of the sulphonamides, which is reversed by 

 2)-aminobenzoic acid, does not affect the respiration of 

 the cells. The secondary effects due to the pyridine 

 or thiazole groups, for instance, which are not reversed 

 by 2>-aminobenzoic acid, are usually concerned with 

 respiratory processes. 



Fildes showed that the growth of Esch. coli and of 

 Eberthella typJiosa was inhibited by indole -acrylic acid, 



/\| -CH =CH.COOH 



i{ 11 , but not by other indole 



NH 

 derivatives and that the inhibition was removed by the 



addition of traces of tryptophane, ^\ CH2.CH.COOH 



II 11 Tshr 

 NH 



^\ 



but not by indole, II II . It is, therefore, assumed 



NH 



that the indole -acrylic acid interferes with the synthesis 

 of tryptophane from indole. By analogy of the equiva- 

 lence of a-naphthyl-acetic acid and indole-acetic acid 



