THE ART OF SCIENTIFIC INVESTIGATION 



The following up of this clue led to the important discovery 

 of the value of Bordeaux mixture in protecting fruit trees and 

 vines from many diseases caused by fungi. ^^ 



(7) The property of formalin of removing the toxicity of 

 toxins without affecting their antigenicity was discovered by 

 Ramon by chance when he was adding antiseptics to filtrates 

 with the object of preserving them/^ 



(8) The circumstances leading to the discovery of penicillin 

 are widely known. Fleming was working with some plate cultures 

 of staphylococci which he had occasion to open several times 

 and, as often happens in such circumstances, they became con- 

 taminated. He noticed that the colonies of staphylococci around 

 one particular colony died. Many bacteriologists would not 

 have thought this particularly remarkable for it has long been 

 known that some bacteria interfere with the growth of others. 

 Fleming, however, saw the possible significance of the observa- 

 tion and followed it up to discover penicillin, although its 

 development as a therapeutic agent was due to the subsequent 

 work of Sir Howard Florey. The element of chance in this 

 discovery is the more remarkable when one realises that that 

 particular mould is not a very common one and, further, that 

 subsequently a most extensive, world-wide search for other anti- 

 biotics has failed to date to discover anything else as good. It 

 is of interest to note that the discovery would probably 

 not have been made had not Fleming been working under 

 " unfavourable " conditions in an old building where there was 

 a lot of dust and contaminations were likely to occur."^ 



(9) J- Ungar^^ found that the action of penicillin on 

 certain bacteria was slightly enhanced by the addition to the 

 medium of paraminobenzoic acid (PABA). He did not explain 

 what made him try this out but it seems likely that it was 

 because PABA was known to be an essential growth factor for 

 bacteria. Subsequently, Greiff, Pinkerton and Moragues'*' tested 

 PABA to see if it enhanced the weak inhibitory effect which 

 penicillin had against typhus rickettsiae. They found that 

 PABA alone had a remarkably effective chemotherapeutic action 

 against the typhus organisms. " This result was quite unex- 

 pected," they said. As a result of this work PABA became 

 recognised as a valuable chemotherapeutic agent for the typhus 



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