436 A MANUAL OF BACTERIOLOGY 



acid and of gas. In their behaviour as regards aggluti- 

 nation, and particularly absorption with specific immune 

 serums, the paratyphoid bacilli also differ markedly 

 from the typhoid bacillus and from one another, and 

 this is the only reliable method for distinguishing them 

 from one another and from other somewhat similar 

 organisms. Bacillus paratyphosus A produces less gas in 

 glucose media than B. paratyphosus B (with some strains 

 very little gas is produced) ; with para A milk remains 

 acid for a fortnight and then becomes alkaline ; with 

 para B it becomes alkaline after a transient acidity ; and 

 though para A changes neutral red to yellow, the red 

 colour tends to return after three weeks or so, while with 

 para B the yellow colour is permanent. That is to say, 

 in its reactions para A is more closely allied to the typhoid 

 bacillus than is para B. Para B, however, blackens a 

 lead acetate medium, while para A does not. On these 

 and other grounds the para B bacillus is regarded as 

 being more allied to the Gartner group than is the 

 para A bacillus (see p. 444). 



During the last two or three years another group of 

 infections has been differentiated caused by a bacillus 

 which has been named para c. Culturally it resembles 

 the para B bacillus, litmus milk becoming alkaline on 

 the fifth to seventh day, but serologically it is quite dis- 

 tinct from the latter. On isolation, para c bacillus is 

 inagglutinable with typhoid, para A, para B and Gartner 

 sera of high titre even in low dilution 1 (see also 

 p. 444). 



B. paratyphosus A infection is relatively common in 

 the East, but paratyphoid fever in Great Britain and 

 Western Europe is commonly caused by para B. Para c 

 infections are likewise Eastern and have been met with 

 in Turkey, Anatolia, Mesopotamia and West Africa. The 



1 W. MacAdam, Lancet, 1919, vol. ii, p. 189. 



