364 THE DYSENTERY BACILLUS 



by the bacillus causing the infection and by all other types of dysentery bacilli. 

 In human subjects the immune body makes its appearance about the fifth to 

 the seventh day of the disease. It is quite distinct from the agglutinin and 

 may be present in the serum before the latter. 



SECTION IV. DETECTION, ISOLATION AND IDENTIFICATION OF 

 THE DYSENTERY BACILLUS. 



To ensure the detection of the bacillus in a case of dysentery it is necessary 

 to examine a recently evacuated stool. The bacilli are most numerous in 

 the latter during the first week of the disease, but subsequently diminish 

 in number, and finally disappear altogether as soon as the stools resume 

 their normal consistency. Bacilli cannot be found in the stools after the 

 twenty-first day of the disease (Rosenthal). 



Dysentery bacilli may occasionally be found in the mesenteric glands and 

 very exceptionally in other organs. 



The bacilli cannot be differentiated by microscopical examination alone 

 and cultures must be sown in every case. 



Select a flake of sero-sanguinolent matter and after washing it thoroughly 

 in sterile water emulsify in a little broth ; use the emulsion for sowing gelatin 

 or agar plates. Plates may also be sown by smearing the surface of the 

 medium with one of the flakes after washing it. Should there be no mucous 

 flakes dilute a trace of the stool in broth. 



(i) Gelatin plates should be sown by the dilution method (p. 78) and incu- 

 bated at 22 C. After 2 or 3 days the surface colonies are examined and any 

 which resemble colonies of the dysentery bacillus picked off for further 

 tests. 



(ii) The best method is to use a lactose-agar medium Chantemesse's(p. 407), 

 Conradi-Drigalski's (p. 407), Endo's (p. 408) [or M'Conkey's (p. 412)]. 



Dip a fine sterile camel-hair brush in the broth emulsion and smear the sur- 

 face of a number of plates of this medium without recharging the brush. It is 

 perhaps even better to smear the surface of the medium with a washed mucous 

 flake and spread the material with a Drigalski's spatula (p. 407). Incubate 

 at 37 C. When examined after 20-24 hours colonies of the colon bacillus 

 will appear as red spots, while those of the dysentery bacillus and of some 

 other organisms will not have altered the colour of the medium. From 

 among the latter pick off those which have a translucent iridescent appear- 

 ance with irregular margins and the centres of which are rather more opaque 

 than the edges, and sow them in broth and other media. Dysentery bacilli 

 will be recognized by the absence of motility, by the cultural characteristics 

 mentioned above and by their being agglutinated by a specific serum. [For 

 purposes of identifying bacilli of the Flexner type the serum of an animal 

 immunized with the Y bacillus is the most generally useful (Morgan).] 



Serum diagnosis. 



Since specific agglutinins are present in the serum of patients suffering from 

 dysentery it is possible to make a diagnosis by the serum reaction. 



Knowing that the serum of patients only agglutinates the bacillus which 

 is causing the infection the serum must be "tested both with a Shiga bacillus 

 and with a Flexner bacillus. The reaction towards che Shiga bacillus should 

 be tested in the first instance with a dilution of 1 in 20 or 1 in 30 ; a positive 

 result under these conditions will be conclusive. The reaction towards 

 bacilli of the Flexner type should be tested in a dilution of 1 in 80 ; agglutina 



