382 TYPHOID FEVER 



case to note the action of a typhoid serum on an organism under 

 investigation, and also the action on the typhoid bacillus of an 

 antiserum to the unknown organism. 



The Paratyphoid Bacillus. This organism, which was when 

 first described often called the paracolou 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. Gywnn 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 para- 

 typhoid 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. Several strains showing slight differences 

 in culture reactions have been obtained. Of these the two 

 chief are " paratyphoid A " and " paratyphoid B," the latter 

 being of commonest occurrence ; these appear to present slight 

 cultural differences. On gelatin, agar, and potato, A resembles 

 b. typhosus, B resembles b. coli ; in litmus milk A produces 

 slight permanent acidity, while after the third day, in the case 

 of B, acidity gives place to alkalinity ; on sugars the ferment- 

 ative activity of B is greater than that of A. Generally speak- 

 ing, the characters of both are those of the group to which they 

 belong. With regard to 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 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 fmaximal clumping dilutions corre- 

 spond, 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 the case is likely to be paratyphoid fever. With 

 regard to the effects of other sera on the paratyphoid bacillus, 

 it may be said that usually a typhoid serum will require to be 

 used in greater concentration to clump this bacillus than is 

 necessary to obtain an effect with the typhoid bacillus itself. 

 Similar effects are observed when the sera of animals immunised 



