ANTIBIOTICS 171 



whicli is /:?-metlioxy-y-liydr(.)xy-}/-/6(yj[)ropylicleiic tutnjiiic 



HO.C==C.R 

 acid. Other tetronic acids produced l)y fungi, j^i ^n qq 



'\o/ ' 



such as carlic, carolic, carolinic and carlosic acids (see 



("H 

 p. 290) and dihvdropenicillic acid, \ 



^ ' ^ ^ >CH.C.OH CO, 



CH3 \o / 



are not antil)acterial. The somewhat similarly constituted 



CO 



CH C.OH 



koiic acid, II II (see p. 294) is much less 



CH,OH.C CH 







active than penicillic acid. 



It is possible that penicillic acid is active because 

 it combines with such amino -acids as glycine, alanine 

 and p-aminobenzoic acid, all of which reverse its effect. 



Penicillin. — In 1929 Fleming noted that the growth 

 of Staph, aurevs on a plate contaminated by Penicillium 

 notatum was inhibited in the neighbourhood of the 

 mould. He showed that the growth of P. notatum on 

 a fluid medium gave a culture filtrate which was strongly 

 bacteriostatic to certain Gram -positive bacteria. The 

 active substance, penicillin, which is also formed by 

 P. chrysogenum and A. flavus, can be extracted from 

 acidified culture filtrates ^vith ether or other organic 

 solvents in the cold and can be taken back into aqueous 



