120 SUPPOSED INSTANCES [ch. ix 



No B. typhosus could be isolated and at later examinations 

 only B. coli was recovered. 



Criticism. Conditions of growth inimical to the life of an 

 organism might be expected to deprive it gradually of its 

 functions. A strain of typhoid bacilli whose vitality is at its 

 lowest ebb would hardly be likely to ferment sugars vigorously, 

 if at all. In both these experiments two factors were at work 

 inimical to the life of B. typhosus, namely the presence of 

 B. coli, and growth in water — a non-nutrient medium. After 

 10 days, in the first experiment, slight fermenting power 

 persisted. After two months, in the second experiment, all 

 fermenting power was lost. No attempt was made to resusci- 

 tate the strain of organisms on ordinary media to ascertain 

 whether with returning vitality fermenting power would be 

 restored. 



That this explanation is the true one and that no new race 

 of organisms was produced is suggested further by the obser- 

 vation that no organisms giving the ordinary reactions of B. 

 typhosus survived side by side with the non-fermenters and 

 that, at a later stage, the strain was found to have died out 

 altogether. 



{d) The change from B. typhosus to Streptococcus faecalis 

 in the peritoneal cavity of the guineapig. 



(Page 230, exp. 4.) The urine of a typhoid carrier "S" 

 was plated and found to contain typhoid bacilli. One colony 

 was subcultured on agar and a standard loopful of a 24 hours' 

 growth was injected into the peritoneal cavity of a guineapig. 

 The animal was found dead in the morning. No typhoid ba- 

 cilli were found in the peritoneal fluid which contained a pure 

 culture of a Gram-positive streptococcus giving the reactions 

 of S. faecalis. 



(e) The change in the peritoneal cavity of a guineapig 

 from B. typhosus to a coliform orgamism giving atypical re- 

 actions. 



The urine of a typhoid carrier " I " was plated after being 

 kept 12 months in a flask. Two colonies of B. typhosus were 

 planted on agar and labelled ZB, and IB^ respectively. 



(e i) (Page 230, exp. 6.) One standard loopful of a 24 hours' 



