BACILLUS TYPHOSUS. 175 



On lactose -litmus agar colonies arc pale blue. On potato 

 the growth is exceedingly variable, and not characteristic, as 

 formerly believed. Sometimes it is scarcely appreciable, at 

 other times it forms a film like a thin veil of the same color 

 as the potato itself. Again, at times the growth is somewhat 

 luxuriant and of a whitish color. It does not coagulate milk. 

 It does not cause fermentation in glucose-, lactose-, or sac- 

 charose-bouillon, although it causes acid formation in glu- 

 cose, but not in lactose or saccharose media. For isolating 

 Bacillus typhosus from blood, Conradi's bile medium is to be 

 recommended. For isolation from water, urine, or fasces 

 Jackson's medium gives better results (see section on Culture- 

 media for these media). It does not produce indol in such 

 quantity as is detected by the ordinary tests. 



Vitalityv It is killed by an exposure of ten minutes to 

 60 C., and in much shorter time by exposure to higher tem- 

 peratures. In the dried conditions it may be preserved for 

 months. 



Agglutination. Persons who have suffered from an attack 

 of typhoid fever or animals which have been inoculated with 

 cultures of this bacillus have generated in their blood-serum 

 a substance called agglutinin. This agglutinin has the prop- 

 erty when mixed with cultures of the Bacillus typhosus of 

 suddenly arresting the motion of the bacilli and of causing 

 their clumping or agglutination, which is quite characteristic, 

 and is made use of for the diagnosis of typhoid fever, as 

 will be described later. Precipitins and lysins have also been 

 demonstrated. 



Pathogenesis. None of the lower animals, as far as has 

 been ascertained, is naturally susceptible to contract or 

 develop typhoid fever. Indeed, the typical lesions of the 

 disease as found in man have rarely been induced in the 

 .lower animals by inoculations with the typhoid bacillus. 



Intraperitoneal, subcutaneous, and intravascular inoculations, 

 in rabbits, guinea-pigs, and mice, will produce marked infec- 

 tion even in those animals, in the form of general septicaemia, 

 in which the bacilli have been recovered in the general cir- 

 culation and in the internal organs. The feeding of aiamuls 



