PARATYPHOID BACILLUS 335 



a low degree of susceptibility on the part of the individual or to 

 a want of pathogenicity in the cultures. 



The Paratyphoid Bacillus. This organism, which was when 

 first described often denominated the paracolon bacillus, was 

 primarily isolated from abscesses occurring in apparently non- 

 typhoid cases. Widal noted its resemblances to b. typhosus and 

 b. coli, from the latter of which it differed in not producing 

 indol and in not fermenting lactose. Gwynn first isolated it 

 from the blood of a case presenting typhoid symptoms, and since 

 then it has been recognised as being the probable cause of the 

 disease effects in about 3 per cent of cases which clinically are to 

 be described as typhoid fever. The case-mortality in paratyphoid 

 fever is low, being only from 1 to 2 per cent. The organism 

 has been isolated from the blood, the roseolar spots, and from 

 the stools, plates of MacConkey's bile -salt neutral -red agar 

 with 1 per cent lactose added being recommended for use here. 

 Several strains showing slight differences in culture reactions 

 have been obtained. Generally speaking, the cultural reactions 

 resemble those of b. coli, though the growth on potato some- 

 times presents typhoid characteristics. It produces no indo], 

 or at least (with some strains) merely a trace, and its action 

 on sugars also differs. With regard to the latter, different 

 results have been obtained by different observers, but there is 

 general agreement that, like the b. coli, it produces acid and gas 

 in glucose, l^vulose, sorbite, mannite, dextrin, maltose, dulcite, 

 galactose, and arabinose; but in lactose, like typhoid, it either 

 originates no change or only slight acid production without any 

 gas formation. It also causes no change in cane sugar, erythrite, 

 salicin, inulin, and raffinose. Probably the most important 

 reactions which will in any case aid in the recognition of the 

 paratyphoid bacillus are the agglutinating reactions. The 

 serum of a paratyphoid patient will agglutinate the bacillus in 

 high dilutions. Observations on the behaviour of such sera 

 towards the b. typhosus have in different cases yielded some 

 discordant results, but to speak generally, it may be said that 

 usually a very much stronger concentration is necessary to give 

 clumping, and often a paratyphoid serum will not clump the 

 typhoid bacillus except in such concentrations as might give 

 similar effects when normal sera are under observation. When 

 any serum clumps both the paratyphoid and the typhoid bacilli 

 the more closely the maximal clumping dilutions correspond, the 

 more likely is the case to be typhoid fever ; on the other hand, 

 if a high dilution will clump the paratyphoid bacillus, while 

 a low dilution is necessary for the typhoid bacillus, then 



