12 THE SCOPE OF THE ENQUIRY [CH. i 



also derived from water, under the term Bacillus typhosm 

 simulans. 



One organism, for example, described by Wilson (1910), 

 resembled B, typhosus in forming acid without gas in glucose 

 and in failing to ferment lactose at 37 C. ; but it failed to 

 agglutinate with typhoid serum, and it resembled B. coli in 

 producing acid and much gas from mannite and in fermenting 

 lactose at 22 C. 



The Bacillus perturbans of Klotz was agglutinated by 

 high dilutions of typhoid serum (1-1550 in 15 minutes) and 

 it produced slight acidity in milk without coagulation ; but it 

 differed from B. typhosus in fermenting both lactose and 

 saccharose, in giving the neutral red reaction and forming 

 indol, and in other ways. 



Major Hor rocks obtained from the urine of a patient 

 convalescent from typhoid fever a typical strain of B. typhosus 

 which however on subculture gave rise to an organism inter- 

 mediate in its characters between B. typhosus and B. coli 

 (vide p. 118). 



4. Slight changes in closely allied organisms, i.e. the 

 possibility in the case of closely allied organisms of a modifica- 

 tion in the few distinguishing features they possess, so that 

 they may appear to change, the one into the other. For 

 example Schmitt (1911) concluded from his experiments that 

 paratyphoid bacilli of the 'Fliigge' type and of the 'Gaertner' 

 type, generally regarded as distinct species, could be trans- 

 formed from one into the other in the animal body. 



5. A complete change in characters, i.e. the possibility of 

 the occurrence, more or less suddenly, of a complete change 

 simultaneously of all the characters of an organism, or at least 

 of all the fundamental ones by which it was distinguished. 

 For example, Major Horrocks (1911) concluded that he had 

 been able gradually to modify a strain of B. typhosus, by 

 changes in its environment, to such an extent that it assumed 

 eventually the characteristics of a Gram-positive coccus having 

 the cultural characters of Streptococcus faecalis. 



Before these several possibilities are studied more fully, 

 the conditions which modify the characters of bacteria will be 

 mentioned and examples given under each head. 



