384 TYPHOID FEVEH 



produce i.ndol, while the latter do. Forms intermediate between 

 the two groups occur, and special attention has been directed to 

 a " Y " strain which does not ferment maltose. There is never 

 any evolution of gas observed in sugar media. 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 Shiga's original 

 observations on thirty-six cases examined, he obtained his 

 bacillus 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 may be 

 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. As the b. dysenterite 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 mucosa, is often lost in the exudation. Sometimes 

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

 mucosa, with 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. In the stools the presence of a 

 large number of degenerated polymorpho-nuclear leucocytes and 



