394 TYPHOID FEVER 



members of the paratyphoid group. Dean prepares his antigen 

 by emulsifying a free surface growth in saline, killing it by an 

 hour's exposure at 60 C. and then alternately freezing it and 

 shaking it in the thawed condition with glass beads, the pro- 

 cedure occupying several days. Finally, the emulsion is centri- 

 fuged and the superjacent fluid constitutes the antigen. Carefully 

 adjusted experiments with different dilutions of antigen and 

 antiserums are necessary, as a quantitative relationship exists 

 between the two substances and excess of either is unfavourable 

 to optimum complement fixation. 



The Bacillus Paratyphosus. This organism, which was 

 when first described often called 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 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. typho- 

 sus, 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 fermentative 

 activity of B is greater than that of A. Generally speaking, 

 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 maximal 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 



