ANTIBIOTICS 



147 



their activity to an effect on some enzyme system in the cell it could be argued that 

 some of them can give rise to structural analogues in vivo. The inactivations of 

 enzyme systems produced by heavy metals reacting with thiol groups, by carbon 

 monoxide with haemoglobin, or by phenol with proteins might be ruled out as 

 analogue inhibitions, but it is possible that the effect of some agents may be due to 

 vital synthesis of inhibitory structural analogues. 



The development of resistance to drugs will be discussed in a later section on 

 antibiotics. 



DIAMIDINES 



Following the observation that aliphatic diamidines w^ere active trypanocidal 

 agents (King, Lourie and Yorke, 1938), Ewins, Ashley, Newbery and their colleagues 

 have evolved a series of aromatic amidines with promising effects, although their 

 toxicity limits their use in treating C. diphthericB infections (Hewitt, 1948). 



VIRUSES AND BACTERIOPHAGE 



Substances inhibiting succinic dehydrogenase have been found to inhibit the 

 multiphcation of bacterial viruses. One difficulty in this w^ork is to separate the effect 

 on bacterial multiplication from the effect on bacteriophage development. The 

 inhibition of development of the Tg phage oi Eskerichia coli strain B has been studied 

 by Czekalowski and Dolby (1949) who report the following inhibitions : — 



ANTIBIOTICS 



The distinction between chemotherapeutic agents and antibiotics is wholly 

 artificial and mainly historical. In general an antibiotic is a substance produced by 

 one micro-organism which antagonises the growth of another micro-organism. Useful 



