378 A MANUAL OF BACTERIOLOGY 



form of dysentery, but not by the amoebic form (unless a 

 double infection be present, which occasionally is the case). 

 The agglutination reaction is obtained in dilutions of 1 

 in 10 to 1 in 100, but may occur only with the particular 

 strain causing the infection. 1 Thus by the agglutination 

 reaction variations between different strains of the B. 

 dy sentence may be detected. 



Pathogenic action. The organism seems limited to the 

 bowel and its mucous membrane and does not gain access 

 to the blood. No characteristic lesions are produced in 

 animals by administration of the dysentery bacillus per os. 

 In man, cultures given by the mouth are stated to have 

 induced a typical dysentery. Animals such as rabbits, 

 guinea-pigs and mice are very sensitive to injections of 

 living and killed cultures ; in fact, it is very difficult to 

 immunise animals against the organism. Amounts of 

 0*1-0'2 mgrm. of an agar culture given intravenously 

 or intraperitoneally are fatal to these animals. 



In man the organism is abundant in the bloody mucoid 

 discharge from the bowel, and at an early stage is easy to 

 isolate by means of Conradi-Drigalski agar plates, on which 

 it forms small transparent blue colonies ; at a later stage 

 (after two to three days) the other organisms in the bowel 

 multiply to such an extent that isolation may become 

 very difficult. " Carriers " occur and help to spread the 

 disease, which may be conveyed by infected water and 

 food and by flies. 



Toxins. The nitrate of dysentery cultures (four to six 

 weeks old) in a somewhat highly alkaline broth (broth 

 just alkaline to litmus + 7 c.c. normal NaOH per litre) is 

 markedly toxic, O'l c.c. being a fatal dose for a large 

 rabbit. 2 



Anti-serum and vaccine. The serum of horses immu- 



1 See Hewlett, Trans, Path. Soc. Lond., vol. Iv, 1904, p. 51. 



2 Todd, Journ. of Hygiene, vol. iv, 1904, p. 480 (Bibliog.). 



