BACILLUS DYSENTERIC 385 



and Duval in the United States. It is now further recognised 

 that the epidemics of dysentery which from time to time occur 

 in lunatic asylums are usually due to bacilli of this type, and in 

 America the organism has been demonstrated in summer 

 diarrhoea in children. The evidence for the relationship of the 

 organism to the disease consists chiefly in the apparently con- 

 stant presence of the organism in the dejecta in this form of 

 dysentery, and the agglutination of the organism by the serum 

 of patients suffering from the disease, but confirmatory evidence 

 has also come from animal experimentation. From different 

 epidemics a great many different strains of the dysentery bacillus 

 have been obtained, but these all possess common characters and 

 'are undoubtedly closely related to one another. The various 

 strains resolve themselves into two chief groups, whose differences 

 lie in their behaviour towards certain sugars, in their capacities 

 of forming indol, and in their agglutinating reactions. The 

 relation of amoebae to dysentery will be discussed in the 

 Appendix. 



Bacillus Dysenteriae. Morphological Characters. This 

 bacillus morphologically closely resembles the typhoid bacillus, 

 but is on the whole somewhat plumper, and filamentous forms 

 are comparatively rare. Involution forms sometimes occur, 

 especially in glucose agar. Most observers have found no trace 

 of motility, whilst others say that it is slightly motile. Vedder 

 and Duval have, however, by a modification of Van Ermengen's 

 process, demonstrated in the case of one strain the presence of 

 numerous lateral flagella, which are of great fineness, but of 

 considerable length. No spore formation occurs ; the organism 

 is stained readily by the ordinary dyes, but is decolorised by 

 Gram's method. 



Cultural Characters. In these also considerable resemblance 

 is presented to the typhoid bacillus. In gelatin a whitish line of 

 growth occurs along the puncture, but the superficial film-like 

 growtli is usually absent, or at least poorly marked. In plate 

 cultures also the superficial growths are smaller and have less of 

 the film-like character, than those of the typhoid organism. On 

 ayar, growth occurs as a smooth film with regular margins, but 

 after two or three days, especially if the surface be moist, Vedder 

 and Duval describe an outgrowth of lateral offshoots on the 

 surface of the medium. On agar plates the colonies resemble 

 those of the typhoid organism, being of smaller size and less 

 ')iaijue than those of the bacillus coli. In peptone bouillon a 

 uniform haziness is produced. As has l^een indicated, different 

 strains of the bacillus behave differently towards different suyarx, 



2 5 



