352 



THE STUDY OF EVOLUTION 



A pure culture of B. typhosus was obtained from Colonel Harvey 

 of the Royal Army Medical College. This organism was found to 

 agglutinate specifically in 1-5000 dilution. Fermentation tests were 

 then done and observations made for several days, and it was found 

 to ferment only mannite and glucose (see Chart I.). Azolitmin broth 

 (sugar free) was used as a base, and the different sugars added to this 

 medium. 



CHART I 

 (Acid Production) 



Now, the question at issue seemed to be whether by reducing the 

 nutriment in the culture medium, i.e. the peptone, and at the same 

 time adding a non-fermentescible sugar, the organism would grow 

 by adapting itself to the food present in the medium. This would 

 be shown by fermentative reactions. 



A culture medium of very low nutritive value was prepared as 

 a base, i.e. 0.5 cc. sugar-free peptone broth, added to 100 cc. of 

 distilled water, sterilized, and coloured with azolitmin. Cultures 

 of B. typhosus sown in this medium grew very slowly, but by 

 adding a fermentescible sugar in even a very small amount, growth 

 became much more rapid with prompt change in colour from 

 blue to red. By adding a non-fermenting sugar the growth was 

 very slow. 



It was decided at first to gradually withdraw a fermentescible 

 sugar from the medium, and to substitute one non-fermentescible, 

 and to plate at daily intervals. Because of the short time at our 

 disposal this was only continued for a few days, but the results were 

 encouraging. 



The following procedure was finally adopted : 



100 cc. flasks of dilute peptone broth were prepared as above, 

 and 1 per cent isodulcite added, this being non-fermentescible, and 

 the whole sterilized on three successive days with steam, and azolitmin 

 added to colour. At the same time azolitmin-isodulcite agar was 

 prepared, only sugar-free broth being used. 



Several flasks of dilute azolitmin isodulcite broth were inoculated 

 with B. typhosus. In 24 hours any change in reaction was noted, 



