APPENDIX 



group of fevers, against which previously nothing had been 

 found effective. 



In the chapter on hypothesis I have described how 

 salvarsan and sulphanilamide were discovered following an 

 hypothesis that was not correct. Two other equally famous 

 chemotherapeutic drugs were discovered only because they 

 happened to be present as impurities in other substances which 

 were being tested. Scientists closely associated with the work 

 have told me the stories of these two discoveries but have asked 

 me not to publish them as other members of the team may not 

 wish the way in which they made the discovery to be made 

 public. Sir Lionel Whitby has told to me a story of a slightly 

 different nature. He was conducting an experiment on the then 

 new drug, sulphapyridine, and mice inoculated with pneumo- 

 cocci were being dosed throughout the day, but were not treated 

 during the night. Sir Lionel had been out to a dinner party 

 and before retuminsr home visited the laboratorv to see how the 

 mice were getting on, and while there lightheartedly gave the 

 mice a further dose of the drug. These mice resisted the 

 pneumococci better than any mice had ever done before. Not 

 till about a week later did Sir Lionel realise that it was the 

 extra dose at midnight which had been responsible for the 

 excellent results. From that time, both mice and men were 

 dosed day and night when under sulphonamide treatment and 

 they benefited much more than under the old routine. 



(lo) In my researches on foot-rot in sheep I made numerous 

 attempts to prepare a medium in which the infective agent would 

 grow. Reason led me to use sheep serum in the medium and 

 the results were repeatedly negative. Finally I got a positive 

 result and on looking back over my notes I saw that, in that 

 batch of media, horse serum had been used in place of sheep 

 serum because the supply of the latter had temporarily run out. 

 With this clue it was a straightforward matter to isolate and 

 demonstrate the causal agent of the disease — an organism which 

 grows in the presence of horse serum but not sheep serum ! 

 Chance led to a discovery where reason had pointed in the 

 opposite direction. 



(ii) The discovery^ that the human influenza virus is able to 

 infect ferrets was a landmark in the study of human respiratory 



163 



