158 TYPHOID FEVER. 



irregularly notched, resembling droplets of oil. In gelatin 

 stab-cultures they appear as small thick disks, finely dentated, 

 of a pearl-like color. They do not liquefy gelatin. 



On agar plates they appear as round, irregular, shiny colo- 

 nies of a blue or grayish-white color, and develop very abun- 

 dantly. In agar stab-cultures the growth is chiefly on the 

 surface, and in the depth of the medium there is scarcely any 

 appreciable development. 



On lactose-litmus agar colonies are 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. It does not produce indol in such quantity as 

 is detected by the ordinary tests. 



Vitality. 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. 



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, 



