COLOX-TYPHOID INTERMEDIATES 247 



Intermediate Members of the Typhoid-colon Group of Bacilli. 



Until recent years the difficulties attending the differentiation of the 

 various members of the typhoid and colon groups of bacilli have been 

 so great that an accurate study of the varieties has not been possible. 

 The application of the Gruber-Widal reaction to this investigation has, 

 however, served to clear up the field to a great extent, so that at the 

 present time the differentiation is comparatively easy. Gartner's dis- 

 covery of the bacillus enteritidis in 1888 in association with epidemics 

 of meat poisoning first gave impetus to the study of the intermediates. 

 Nocard's work on bacillus psittacosis followed in 1892. In 1893 Gilbert 

 introduced the terms "paracolon" and "paratyphoid" to designate 

 bacilli of this group resembling more nearly in biological characters the 

 colon bacillus on the one hand and the typhoid bacillus on the other, 

 but at that time the organisms now known as paratyphoid bacilli had 

 not been identified. 



The intermediates include bacillus enteritidis and similar organisms 

 recovered from cases of epidemic meat poisoning, the gas-producing 

 typhoid-like bacilli of various observers, bacillus psittacosis, bacillus 

 cholerse suis, bacillus icteroides, bacillus of calf septicaemia, and the 

 various paratyphoid and paracolon bacilli that have been described 

 recently. 



The bacilli intermediate between bacil ! us coli communis and bacillus 

 typhosus can be distinguished without difficulty from either of them. 

 They produce gas in glucose media and in this respect they differ from 

 typhoid, but, unlike bac llus coli communis, they have no power of 

 fermenting lactose, coagulating milk or forming indol. 



They are not agglutinated by typhoid sera except, as in the case of 

 colon bacilli, imperfectly in low dilutions because of group agglutinin. 



Among the intermediates themselves, however, two main groups can 

 be recognized, and it is proposed to call these paracolon and paratyphoid 

 groups, the former appearing in some respects to be more nearly 

 allied to bacillus coli communis and the latter more nearly to typhoid. 



The main points of difference are that the paracolons turn milk and 

 whey alkaline after a short initial acidity and form gas freely in glu- 

 cose media, while with the paratyphoids there is in milk and whey an 

 initial acidity, but no or very slight subsequent alkalinity; the gas 

 production in glucose media is much less pronounced. Neutral red 

 agar also differentiates between the two groups. Like bacillus coli com- 

 munis all the intermediates reduce the color to yellow in twenty-four 

 to forty-eight hours, but with the paratyphoids after four or five days 

 the red color begins to return from above downward until in two or 

 three weeks the medium is again red throughout. With the paracolons 

 the yellow color is permanent. 



Agglutination tests have taught us that the members of the coli com- 

 munis group do not constitute a distinct species as in the case with 

 typhoid bacilli. When these tests are applied to the intermediates it 

 Is found that the members of the paracolon group do not all show mutual 



