404 PATHOGENIC MICROORGANISMS 



t 

 alive after thirteen years. In natural waters it may remain alive as 

 long as thirty-six days, according to Klein.' In ice, according to Prud- 

 den/ it may remain alive for three months or over. Against the ordi- 

 nary disinfectants, the typhoid bacillus is comparatively more resistant 

 than some other vegetative forms. It is killed, however, by 1 : 500 

 bichlorid or five-per-cent carbolic acid within five minutes. 



Pathogenicity. — In animals, some early investigators to the contrary, 

 typhoidal infection does not occur spontaneously and artificial inocula- 

 tion with the typhoid bacillus does not produce a disease analogous to 

 typhoid fever in the human being. Frankel ^ was able to produce intes- 

 tinal lesions in guinea-pigs by injection of the bacilli into the duodenum, 

 and recovered the bacteria from the spleens of the animals after death, 

 but the disease produced was in no other respect analogous to typhoid 

 fever in the human being. It is probable that typhoid bacilli injected 

 into animals do not multiply extensively and that most of the symp- 

 toms produced are due to the endotoxins liberated from the dead bac- 

 teria. In corroboration of this view is the observation that inoculation 

 with dead cultures is followed by essentially the same train of symp- 

 toms as inoculation with live cultures.* The injection of large doses into 

 rabbits or guinea-pigs intravenously or intraperitoneally is usually 

 followed by a rapid drop in temperature, often by respiratory em- 

 barrassment and diarrhea. Occasionally blood may be present in 

 the stools. According to the size of the dose or the weight of the ani- 

 mal, death may ensue within a few hours, or, with progressive emacia- 

 tion, after a number of days, or the animal may gradually recover. 

 Welch and Blachstein ^ have shown that typhoid bacilli injected into 

 the ear vein of a rabbit appear in the bile and may persist in the gall- 

 bladder for weeks. Typhoid bacilli isolated from different sources may 

 show considerable variations in virulence and toxicity. 



Doerr,* Koch,^ Morgan,' and more recently Johnston^ have all 

 confirmed this, the last named showing that the typhoid bacillus could 



1 Klein, Med. Officers' Report, Local Govern. Bd., London, 1894. 



2 PrvMen, Med. Rec, 1887. 



' Frankel, Cent. f. klin, Med., 10, 1886. 



« Petruschky, Zeit. f. Hyg., xii, 1892. 



' Welch and Blachstein, Bull. Johns Hop. Hosp., ii, 1891. 



« Doerr, Centralbl. f. Bakt., 1905. 



' Koch, Zeitschr. f . Hyg., 1909. 



^Morgan, Jour, of Hyg., 1911. 



' Johnston, Jour, of Med. Res., xxvii, 1912. 



