THE ART OF SCIENTIFIC INVESTIGATION 



became standard practice twenty-five years before the bio- 

 chemical processes involved in milk fever were elucidated; 

 indeed the basic cause of the disease is still not understood, 

 nor do we know why the injection of air usually cures the 

 disease/'* *^ 



An hypothesis may be fruitful, not only for its propounder, 

 but may lead to developments by others. Wassermann himself 

 testified that his discovery of the complement fixation test for 

 syphilis was only made possible by EhrUch's side-chain theory. 

 Also the development of the Wassermann test has another 

 interesting aspect. Since it was not possible to obtain a culture 

 of the spirochaete which causes syphilis, he used as antigen 

 an extract of liver of syphiHtic stillborn children, which he 

 knew contained large numbers of spirochaetes. This worked very 

 well and it was not until some time later that it was found that 

 not only was it unnecessary to use syphilitic hver but equally 

 good antigens could be prepared from normal organs of other 

 animals. To this day it is a mystery why these antigens give a 

 complement fixation reaction which can be used to diagnose 

 syphilis, and only one thing is certain : that the idea that 

 prompted Wassermann to use an extract of liver was entirely 

 fortuitous. But since we still see no reasoned explanation, we 

 would probably still have no serological test for syphilis but for 

 Wasserman's false but fruitful idea. 



The foundation of chemotherapy was due to Paul Ehrlich's 

 idea that, since some dyes selectively stained bacteria and 

 protozoa, substances might be found which could be selectively 

 absorbed by the parasites and kill them without damaging the 

 host. His faith in this idea enabled him to persist in the face 

 of long continued frustration, repeated failure and attempts by 

 his friends to dissuade him from the apparently hopeless task. 

 He met with no success until he found that trypan red had some 

 activity against protozoa and, developing further along lines 

 suggested by this, he later developed salvarsan, an arsenical 

 compound effective therapeutically against syphiHs, the six hun- 

 dred and sixth compound of the series. This is perhaps the 

 best example in the history of the study of disease of faith 

 in a hypothesis triumphing over seemingly insuperable difficulties. 

 It would be satisfying to end the story there but, as so often 



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