33 2 SPECIFIC M^IO-ORGANISMS 



spread out and thinner than that of B. coli, and in semi-solid media 

 the growth of B. typhosus may diffuse for quite a distance because 

 of its active motility. Dextrose is fermented with the production 

 of acid but without gas. Lactose is not fermented. Litmus 

 milk is rendered slightly acid and later becomes alkaline without 

 coagulation. On potato the growth is almost invisible. In Dun- 

 ham's pepton-salt solution, indol is not produced in sufficiently 

 large quantities to be detected, but indol can be demonstrated 

 in old cultures in 5 per cent pepton. Growth is most rapid at 

 37~39 C., but occurs also at room temperature. 



B. typhosus is killed by moist heat in 10 to 15 minutes, and by 

 5 per cent carbolic acid or i-iooo mercuric chloride in three to 

 five minutes, when exposed in aqueous suspension. It resists dry- 

 ing for several days and may be alive in dry dust. The longevity 

 of B. typhosus in surface waters has been studied by several in- 

 vestigators without full agreement. In general B. typhosus would 

 seem to survive in such water only for three to ten days except 

 it be taken up by aquatic animals, such as the shellfish, when it 

 may persist for several weeks. In soil and in frozen material 

 the bacillus may live a much longer time. Freezing and thawing 

 destroys a large percentage of the bacilli in a given liquid but 

 does not destroy them all. 



The poisons are intimately associated with the cell substance, 

 and it is not often that culture filtrates are found to be toxic. 

 The dead germ substance is somewhat poisonous, and when it 

 is disintegrated by physical comminution or by digestion with 

 dilute alkali at a high temperature, or by the action of serum 1 

 upon it, there are set free quite powerful poisons or perhaps differ- 

 ent quantities of the same poison. 



The various small laboratory animals are very susceptible to 

 intraperitoneal inoculation with B. typhosus and usually die in 

 24 to 48 hours with acute peritonitis and bacteremia. The dis- 

 ease produced bears no resemblance to typhoid fever in man. 

 In chimpanzees a very typical attack of typhoid fever has been 

 1 Zinsser: Journ. Exp. Med., 1913, Vol. XVII, pp. 117-131. 



