THE ART OF SCIENTIFIC INVESTIGATION 



the group in the protein with which the glyoxylic acid reacted, 

 and this led him to his famous isolation of tryptophane.^* 



When Weil and Felix were investigating cases of louse-borne 

 typhus in Poland in 19 15 they isolated the bacterium known as 

 " Proteus X " from some patients. Thinking it might be the 

 cause of the disease they tried agglutination of the organism 

 with the patients' sera and obtained positive results. It was then 

 found that Proteus X was not the causal organism of the disease ; 

 nevertheless agglutination of this organism proved to be a reliable 

 and most valuable means of diagnosing typhus. In the course 

 of their experimental study of this serological reaction Weil and 

 Felix identified the O and H antigens and antibodies, and this 

 discovery in turn opened up a completely new chapter in serology. 

 Later it was found that in Malaya those cases of typhus con- 

 tracted in the scrub failed to show agglutination to Proteus X19. 

 Strangely enough a new strain of Proteus, obtained from England 

 and beUeved to be a typical strain of Proteus X19, agglutinated 

 with sera from cases of scrub typhus but not with sera from the 

 cases contracted in the town (shop typhus), which were reacting 

 satisfactorily with the Proteus X19 strain that had been used in 

 many parts of the world. Later it transpired that scrub typhus 

 and shop typhus were two different rickettsial diseases. How it 

 came about that the strain of Proteus sent out from England 

 was not only not typical Proteus X19, but had changed to just 

 what was wanted to diagnose the other disease, remains a 

 profound mystery. ^^ 



Agglutination of red blood cells of the chick by influenza virus 

 was first observed quite unexpectedly by Hirst and independently 

 by McClelland and Hare when they were examining chick 

 embryos infected with the virus. Fluid containing virus got mixed 

 with blood cells which became agglutinated and the alert and 

 observant scientists quickly followed up this clue. The discovery 

 of this phenomenon has not only revolutionised much of our 

 technique concerned with several viruses, but has opened up a 

 method of approach to fundamental problems of virus-cell 

 relationships.^^' ^" Following this discovery, other workers tried 

 haemagglutination with other viruses and Newcastle disease, fowl 

 plague and vaccinia were found to produce the phenomenon. 

 However it was again by chance observation that haemagglutina- 



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