Vitamins and Antivitamins 33 



antagonists. A large number of vitamin antagonists have been made, 

 which do in fact interfere with the growth of bacteria; but in most 

 cases they are nearly as harmful to animals as to the bacteria. 



There is, however, one case in which successful use is made of an 

 antagonist, and this is the basis of the well-known 'sulphur' drugs 

 (sulphanilamides). These were discovered by trial and error. Until 

 recent years there was very little to guide chemists in the search for 

 valuable drugs. Enormous numbers of compounds have been made 

 and tested; some had curative properties, but no one knew why. This 

 group of drugs was discovered after long research to be extremely 

 effective in some kinds of infections. The reason for this was not 

 clear at once. Then it was discovered that a somewhat similar sub- 

 stance, p- amino-benzoic acid (pab for short), interfered with the 

 bactericidal action of the drug (for formulae, see Appendix, p. 164). 

 If PAB is administered with the drug, much larger doses have to be 

 used to produce the same effect. This suggested to Fildes and Woods 

 that the 'sulphur' drugs were really antagonists of pab. At this time 

 PAB had not been recognized as a vitamin, but its presence in many 

 micro-organisms has since been confirmed. It is now known to be a 

 component of fohc acid, a substance which occurs abundantly in 

 green leaves and has a stimulating effect on the growth of some 

 bacteria. Folic acid seems to be concerned in the formation of the 

 highly specialized substances required in the nuclei of cells. The 

 higher animals as well as many of the lower organisms require pab; 

 but it is not known definitely why certain bacteria are more sensitive 

 to PAB antagonists than are the hosts. More recently it has been found 

 that another compound of the same kind (fas = p. -aminosalicylic 

 acid) is very effective in arresting some types of tuberculosis. 



If it were possible to find enzymes in the disease-producing organ- 

 isms which were more sensitive to antagonists than those of the 

 animals, the problem of finding drugs to kill the bacteria would be 

 very simple; but unfortunately this is not usually possible. Drugs 

 which harm the parasite usually injure the host as well. 



The problem of producing substances which will harm bacteria 

 more than their hosts is one which has been solved more effectively 

 by many organisms than by the conscious efforts of scientists. Many 

 living things must have encountered the problem of how to repel the 

 attacks of bacteria and other parasitic forms, and it is perhaps not 

 surprising that those which have survived are provided with chemical 

 protection. The best known of these substances is penicillin, which 

 is produced by a fungus, Penicilliiim notatum, the greenish mould 

 which grows on damp bread. The story of the discovery of penicillin 

 by Sir Alexander Fleming in 1929 has often been told. He noticed 



