BACTERIA PATHOGENIC TO MAN 



the medium, and when scraped with the needle offers a certain resist- 

 ance. In some cases, however, the growth is restricted to the immediate 

 vicinity of the point of inoculation. Again, the growth may be quite 

 heavy and colored yellowish-brown, and with a greenish halo, when 

 it is very similar to the growth of the colon bacillus. These differences 

 of growth on potato appear to be chiefly due to variations in the sub- 

 stance of the potato, especially in its reaction. For the characteristic 

 growth the potato should be slightly acid. A new lot of potato should 

 always be tested with a typical typhoid bacillus as a control. 



INDOL REACTION. It does not produce indol. This test was pro- 

 posed by Kitasato for differentiating the typhoid bacillus from other 

 similar bacilli, such as those of the colon group, which, as a rule, give 

 the indol reaction. 



The typhoid bacillus, like the colon bacillus, produces alkaline 

 substances from peptone. 



NEUTRAL RED. In stick cultures in glucose agar the typhoid bacillus 

 produces no change, while the colon bacillus decolorizes the medium 

 and produces gas. 



EFFECT OF INHIBITING SUBSTANCES IN CULTURE FLUIDS. The 

 typhoid bacillus is inhibited by weaker solutions of formaldehyde, 

 carbolic acid, and other disinfectants, than is the colon bacillus. Most 

 typhoid-like bacilli resemble the typhoid bacillus in this respect. 



ACTION ON DIFFERENT SUGARS. The determination of the action 

 upon sugars of any bacillus belonging to the typhoid or colon group is 

 one of the most important of all the cultural differential tests. It has 

 been considered in detail in connection with the colon group. 



FERMENTATION. While the typhoid bacillus does not ferment glucose, 

 galactose and levulose, it does produce acid from these substances. It 

 evolves gas from none of the sugars. 



MILK. The typhoid bacillus does not cause coagulation when 

 grown in milk. In litmus whey the neutral violet color becomes more 

 red during the first forty-eight hours; the fluid, however, remains clear. 



Production of Disease in Animals. It is impossible experimentally 

 to produce true typhoid fever in animals. Sickness or fatal results 

 without the appearance of the typical pathological changes have regu- 

 larly followed animal inoculations, but in most cases they could easily 

 be traced to the toxaemia produced by the substances in the bodies of 

 the bacilli injected. Typhoid bacilli, freshly obtained from typhoid 

 cases and introduced subcutaneously in animals, rapidly die. In the 

 peritoneal cavity they may increase, causing a fatal peritonitis with 

 toxic poisoning. By accustoming bacilli to the animal body a certain 

 degree of increased virulence for the animal can be obtained, so that 

 smaller amounts of culture may prove fatal. Among the most success- 

 ful efforts in this direction are the experiments of Cygnaeus and Seitz, 

 who, by the inoculation of typhoid bacilli into dogs, rabbits, and mice, 

 produced in the small intestines conditions that were histologically and 

 to the naked eye analogous to those found in the human subject. 

 Their results, however, were not constant. 



