146 ESSENTIALS OF BACTERIOLOGY 



such cases give a positive agglutination reaction, the produc- 

 tion of a curative serum by the immunization of animals 

 with pure cultures, and the results on experiment animals, 

 leave little doubt as to the specificity of the organism. 



Origin. The dejecta of dysenteric patients. 



Form. A plump bacillus with rounded ends, resembling 

 the typhoid and colon bacilli (Fig. 63). 



Properties. Motility doubtful, but numerous flagella have 

 been demonstrated. Does not form spores. 



Staining. Stains readily, negative to Gram; facultative 

 anaerobe. 



Growth. Best at 37 C. Killed by ten minutes' exposure 

 to 55 C. 



Gelatin. A white line of growth along puncture; super- 

 ficial growth slight. 



Bouillon. Uniform clouding. Indol usually not produced ; 

 milk not coagulated. 



A gar. Resembles typhoid bacillus. 



Potato. Thin whitish layer, turning light brown. 



No gas-formation in glucose or lactose media. 



Acid is formed. 



Pathogenesis. Mice and guinea-pigs die in one or two days 

 after intraperitoneal inoculation. Rabbits usually recover, 

 though lesions analogous to those of human dysentery have 

 been produced. Dogs die in five or six days, with well- 

 marked diarrhea. 



Products. The patient's blood-serum agglutinates the ba- 

 cillus in cases in which it can be cultivated from the stools. 

 The reaction is absent from other cases. Shiga has reduced 

 the mortality from 34.7 to 19 per cent, by means of a serum 

 obtained from immunized horses, but in more extensive tests 

 the antidysenteric serum proved of little value. 



In man the organism or some of its varieties is associated 

 with dysentery and is found chiefly in the stools; abscesses 

 are seldom found; the amebic dysentery forms liver abscess, 

 not in other organs. Polluted water is responsible for its 

 spread in epidemic form. 



