368 THE BACILLUS OF TYPHOID FEVER. 



the Bacillus coli communis remains in full possession. According 

 to Wathelet (1895) the colon bacillus will grow in bouillon which 

 has served as a culture medium for the typhoid bacillus, or on the 

 surface of an agar plate from which a typhoid culture has been re- 

 moved; but the typhoid bacillus fails to develop in culture media 

 which have served for the development of the colon bacillus. 



The various diagnostic tests which have been proposed, and the 

 extensive literature of the subject, show that the recognition of the 

 typhoid bacillus in water, faeces, etc., is attended with serious diffi- 

 culties. This is chiefly due to the fact that bacilli have been ob- 

 tained from various sources which resemble more or less closely the 

 typical typhoid bacillus as obtained from the spleen of a typhoid 

 patient (or cadaver) and the " colon bacillus " as found in the alimen- 

 tary canal of healthy men and animals; and also from the fact that 

 the bacillus, as obtained from typhoid cases, varies to some extent in 

 its biological characters, and that varieties may be produced in the 

 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- 

 t induced 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 nu.re or less permanent kind. 



Frankland (18U5), as a result of extended experiments, has arrived 



