236 PUBLIC HEALTH BACTERIOLOGY 



2. Grueber's Reaction. Consists in determining the 

 race of a bacterium by testing it against the blood serum 

 of an animal immunized to an organism of known race. 

 The reaction is the converse of the Widal one, but high 

 dilutions (i-iooo) must be used to avoid error due to 

 group agglutinins. It is open to the fallacies that some 

 bacilli are inagglutinable, though belonging undoubtedly 

 to an agglutinable race (some typhoid bacilli), and bac- 

 teria giving a negative result may nevertheless have 

 very similar pathogenic characters to those giving a 

 positive result. 



Principal Channels of Infection. Water, milk, ice-cream 

 foods, oysters, mussels, water-cress, lettuces, radishes, flies, 

 dust, contact, chronic germ-carriers. 



Paratyphoid Bacilli (also called paracolon bacilli) 

 are the probable cause of a disease clinically resembling 

 mild typhoid (about 3 per cent of cases treated as typhoid 

 are probably paratyphoid). Onset is usually sudden, with 

 chills ; mortality is low (2 per cent), and on post-mortem 

 examination no characteristic ulceration of Peyer's patches 

 is observed. Two chief varieties are described, namely, 

 paratyphoid " A " and paratyphoid " B." Of these B 

 is the more widely distributed in nature, and is more 

 pathogenic to animals, and is believed by some to be the 

 same as B. enteritidis (Aertryck) and B. typhi murium 

 {mouse typhoid) . In cultures A resembles the typhosus ; 

 and B the colon bacillus ; and fermentative reactions like- 

 wise, except in milk, where A gives slight permanent acidity, 

 and B slight acidity which after the third day gives place 

 to alkalinity. Cases of illness due to A, resemble mild 

 typhoid ; and to B, are allied to food-poisoning with 

 severe gastro-intestinal symptoms. Organisms of this 

 group form endotoxins which are heat resisting, and there- 

 fore the ingestion of cooked food containing the bacilli 

 may produce severe disturbance, thus relating them to 

 Gaertner's bacillus (B. enteritidis). None form indol. 

 Ah 1 give fluorescence with neutral-red. These bacilli are 

 motile, flageUar, show agglutination phenomena, and 

 ferment dextrose, dulcite and mannite, but not lactose 

 nor saccharose. They are present at times with the B. 

 typhosus, and may thus produce a mixed infection. 



