THE PROTEUS GROUP 413 



C0 2 to one volume of H 2 . Indole production negative, 

 Voges-Proskauer reaction positive. Capsulation is fre 

 quent, and gelatin sometimes liquefied. B. cloaccu, B. 

 (lactis) aerogenes, and B. pneumonice belong to this group. 



B. wesenbergi is not mentioned. It is intermediate between 

 Group IV and Group V, as it ferments glucose with the production 

 of acid and gas, and lactose with the production of acid only. It 

 is met with in diarrhoea. 



The Voges-Proskauer reaction is obtained by growing the 

 organism in 2 per cent, glucose broth in a fermentation tube 

 (Fig. 12, p. 81) for three days. Strong caustic potash solution 

 is then added, and, on exposure to air, a pink colour develops. The 

 reaction is due to the formation of acetyl-methyl-carbinol. This, 

 in the presence of air and potash, is oxidised into diacetyl, which 

 then reacts with some constituent of the peptone in the medium, 

 giving the pink colour (Harden and Walpole 1 ). 



The Proteus Group 



The Proteus group may conveniently be considered here, 

 although it is sharply distinguished from the Typhoid -Colon 

 group morphologically, by fermenting sucrose but not lactose, 

 by the gas formed consisting mainly of H 2 , and by its vigorous 

 decomposition of proteins. It has recently been the subject of 

 study by Wenner and Rettger. 2 The name "Proteus" signifies 

 changeability of form, derived from the fact that in gelatin (5 per 

 cent.) plates wandering amoeboid colonies occur masses of cells 

 undergoing continual changes in outline and position, and some- 

 times separating from the mother colony (Hauser). The indi- 

 vidual cells are mostly coli-like, 1-5-2-5 p, in length, though 

 occasionally much longer ones occur, and they may form short 

 chains. They are actively motile, non-sporing and Gram -negative. 

 They grow luxuriantly on all the ordinary media at from 20 to 

 37 C. Gelatin is more or less rapidly liquefied, and litmus milk 

 after transient alkalinity is decolorised, curdled, and the clot is 

 finally digested. A luxuriant dirty-brown growth develops on 

 potato, with fishy odour. Fermentation with both acid and gas 



1 Proc. Roy, Soc. Lond., B, vol. Ixxvii, 1906, p. 399. 



2 Journ. Bacteriology, vol. iv, 1919, p. 331. 



