THE COLON, TYPHOID AND DYSESfrERY BACILLI ' 34S 



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 iriotility. Dextrose is fermented with the 

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

 Litmus milk is rendered sUghtly acid and later becomes alkaline 

 without coagulation. On potato the growth is almost invisible. 

 In Dunham's pepton-salt solution, iiidol is not produced in suffi- 

 ciently large quantities to be detected, but indol can be demon- 

 strated 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 at 60° C. 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 drying for several days an,d may be alive in dry dust. The 

 longevity of B. typhosus in surface waters has been studied by 

 several investigators 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^ 

 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 

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



