36 A CONSIDERATION OF THE EVIDENCE [ch. hi 



of 24 hours but after ten days incubation gave a definitely 

 alkaline reaction. 



It is obvious from these facts that the question of the time 

 allowance is of great importance. This point will be considered 

 further in connection with variations in fermenting power 

 (vide p. 66). 



9. Finally, pathological research and dinieal observation 

 must go hand in hand. The former, if it is divorced from the 

 latter, is beset with dangers. 



A certain patient's blood, in the laboratory, may give at 

 one time a positive Widal's test and at another — some weeks 

 later — fail to do so. The knowledge that on the first occasion 

 the patient was the subject of jaundice would suggest a simple 

 explanation (Griinbaum, 1896) for a phenomenon otherwise 

 difficult to elucidate. 



Similarly the knowledge that sodium benzoate was being 

 administered to a patient sufifering from cystitis would aflbrd 

 an explanation of the fact that the strain of B. coli contained 

 in the urine of the patient showed a greatly diminished power 

 of gas production in dextrose (Fenfold, 1911 a). 



Again, altered pathogenicity may be falsely attributed to 

 a strain of organisms if clinical observation is neglected. 

 A certain disease may be latent in a patient — that is to say, 

 present without giving rise to any noticeable symptoms. The 

 constitutional disturbances arising from infection by the 

 organism in question may "light up" this pre-existing disease 

 and the symptoms of the latter then be incorrectly credited 

 to the invading organism. 



