THE BACILLUS OF TYPHOID FEVER. 44? 



bacillus as obtained, from a single colony, by special modes of culti- 

 vation. From a consideration of these facts certain authors have 

 been led to the conclusion that Bacillus typhi abdominalis and Bacillus 

 coli communis are simply varieties of the same species. This view, 

 however, is not generally accepted, and the characters which serve to 

 differentiate the two bacilli are sufficiently well defined when typical 

 cultures are compared. These characters, briefly stated, are: The 

 invisible growth of the typhoid bacillus on potato; its failure to give 

 the indol reaction; its failure to coagulate milk, or to produce a 

 change of color in litmus milk ; its failure to produce gas in culture 

 media containing glucose or lactose; its failure to grow in formalin 

 bouillon (1 : 7,000) ; and its active motility. Whether the closely re- 

 lated bacilli which present some of the characters above indicated, 

 without corresponding in all particulars with typical cultures of the 

 typhoid bacillus, are varieties of this bacillus, which under favorable 

 circumstances could give rise to typhoid infection, has not been defi- 

 nitely determined, but appears to be quite probable. It may be that 

 such varieties are developed when the typhoid bacillus in faeces finds 

 its way into surface waters, under conditions which are favorable for 

 its continued development as a saprophyte. On the other hand, it 

 may be that one or more of the saprophytic bacilli, which are found 

 in water and which closely resemble the typhoid bacillus, may give rise 

 to the infectious disease which we know as typhoid fever when in- 

 troduced into the alimentary canal of a particularly susceptible indi- 

 vidual, and that the special conditions attending its development as 

 a parasite give rise to certain modifications in its biological charac- 

 ters of a more or less permanent kind. 



Frankland (1895), as a result of extended experiments, has arrived 

 at the conclusion that when the typhoid bacillus is cultivated for a 

 long time in media which are more and more largely diluted with 

 water, it acquires an increased ability to survive in river water. 



A predisposition to typhoid infection is established -by various 

 depressing agencies, such as inanition, overwork, mental worry, in- 

 sanitary surroundings, etc. And there is considerable evidence in 

 support of the supposition that exposure to the offensive gases 

 given off from ill- ventilated sewers constitutes a predisposition to 

 the disease. 



Experiments made by Alessi (1894), in the Hygienic Institute 

 of the University of Rome, give support to this view. The ex- 

 periments were made upon rats, guinea-pigs, and rabbits. The 

 rats were confined in a close cage with perforated bottom, which was 

 placed over the opening of a privy; the guinea-pigs and rabbits in 

 similar cages having a receptacle below in which their own excreta 

 was allowed to accumulate. The animals which breathed an atmo- 



