BACILLUS DYSENTERIC 399 



or whitish layer, which, however, in the course of a few days 

 assumes a brownish-red or dirty grey colour, with some discolora- 

 tion of the potato at the margin of the growth. The variants of 

 the dysentery bacillus group themselves chiefly round the Flexner 

 type, from which they are more difficult to differentiate than 

 from the Shiga type. 



Relation to the Disease. The organism has been found in 

 large numbers in the dejecta, especially in the acute cases, where 

 it may be present in almost pure culture. In the thirty-six cases 

 examined, Shiga obtained it in thirty-four from the dejecta, and in 

 the two others post mortem from the intestinal mucous membrane. 

 The organism does not appear to spread deeply or to invade 

 the general circulation. In the more chronic cases it is difficult 

 to obtain, on account of the large number of the bacillus coli and 

 other bacteria present. Vedder and Duval found agar plates to 

 be the best method of culture, these being incubated at the 

 blood temperature. They also found that if the colonies which 

 appeared at twelve hours were marked with a pencil, there was 

 a greater probability of obtaining the bacillus of dysentery from 

 those which appeared later, most of those appearing early being 

 colonies of the bacillus coli. MacConkey's agar medium with 

 lactose added may be used for isolation from stools. A little of 

 the fseces is rubbed up in broth and some of the mixture stroked 

 on the medium. The formation of acid by the b. coli colonies 

 enables them to be excluded, and therefore, as the b. dysenterise 

 is not a lactose fermenter, the colourless colonies which develop 

 after twenty-four hours are picked out for further investigation. 



As already stated, both acute and chronic cases are marked 

 by the presence of this organism. In the former, where death 

 may occur in from one to six days, the chief changes, according 

 to Flexner, are a marked swelling and corrugation of the mucous 

 membrane, with haemorrhage and pseudo-membrane at places. 

 There is extensive coagulation-necrosis with fibrinous exuda- 

 tion and abundance of polymorpho-nuclear leucocytes, and the 

 structure of the mucous membrane, as well as that of the 

 muscularis mucosse, is often lost in the exudation. Sometimes 

 deep ulceration occurs, there is also great thickening of the sub- 

 mucosa, with great infiltration of leucocytes, these being chiefly 

 of the character of plasma cells. In the more chronic forms the 

 changes correspond, but are more of a proliferative character. The 

 mucous membrane is granular, and superficial areas are devoid of 

 epithelium, whilst ulceration and pseudo-membrane are present 

 in varying degree. A feature of bacillary dysentery is the fact 

 that abscess of the liver does not occur as a complication. 



