HYPOTHESIS 



happens, in science, the final note must be one of irony. Ehrhch's 

 search for substances which are selectively absorbed by patho- 

 genic organisms was inspired by his firm belief that drugs cannot 

 act unless fixed to the organisms; but to-day many effective 

 chemotherapeutic drugs are known not to be selectively fixed to 

 the infective agents. 



However the story is not yet finished. Gerhard Domagk, 

 impressed by Ehrlich's early work, tried the effects of a great 

 number of dyes belonging to the group called " azo-dyes " to 

 which Ehrlich's trypan red belonged. Then in 1932 he found a 

 dye of this series, prontosil, which was effective therapeutically 

 against streptococci without damaging the infected animal. This 

 discovery marked the beginning of a new era in medicine. But 

 when the French chemist, Trefouel, set to work on the composi- 

 tion of the drug he was amazed to find its action was in no 

 way due to the fact that it was a dye, but was due to it con- 

 taining sulphanilamide, which is not a dye. Again Ehrlich's 

 false idea had led to a discovery that can justly be described as 

 miraculous. Sulphanilamide had been known to chemists since 

 1 9 08 but no one had any reason to suspect it had therapeutic 

 properties. It has been said that, had its properties been known, 

 sulphanilamide could have saved 750,000 lives in the 191 4-18 

 war alone.* Ehrlich's early work with dyes is said also to be the 

 starting point of the work which led to the discovery of the 

 modern anti-malarial drug atebrin without which the Allies might 

 not have won the war in the Pacific. 



Another group of chemotherapeutic substances which were 

 evolved by following an hypothesis is the diamidine group used 

 against the leishmania v.'hich causes kala-azar. The idea with 

 which the investigation was started off was to interfere with the 

 natural metabolic processes of the parasite, especially with its 

 glucose metabolism, by using certain derivatives of insulin. One 

 of these, synthalin, was found to have a remarkable leish- 

 manicidal action, but in a dilution far higher than could possibly 

 affect glucose metabolism. Thus, although the hypothesis was 

 wrong, it led to the discovery of a new group of useful 

 drugs. 



In certain parts of Great Britain and Western Australia there 

 occurs a nervous disease of sheep known as swayback, the cause 



45 



