108 THE ACTION OF ENZYMES 



the curd having small gas bubbles in it. The organisms when 

 grown in this medium, generally develop capsules. 



Sugars. Glucose, lactose, and saccharose are all fermented 

 with the production of acid and much gas, but it does not 

 ferment dulcite. When Bact. lactis aerogenes is grown for three 

 days in 2 per cent, glucose bouillon in a fermentation tube, and 

 a strong solution of caustic potash then added, a pink or reddish 

 fluorescent colorisation is developed after twenty-four hours : 

 this is known as the Voges-Proskauer reaction. (Ex. 65.) 



5. Another " coliform " organism frequently met with is 

 Bact. cloacae, Jordan. It is one of the common bacteria in 

 sewage, has been isolated from the intestinal canal, and some- 

 times occurs in impure water and dirty milk. This bacterium 

 is motile, and in general morphological characters closely 

 resembles B. coli. The surface colonies in gelatine are thin, 

 whitish, and translucent, with darker centre and wavy outline ; 

 the deeper ones round and yellowish. Gelatine is slowly lique- 

 fied in four to thirty days. Bouillon is rendered turbid in twenty- 

 four hours, generally with slight scum formation. Milk is 

 acidified and coagulated in ten to eighteen days. It ferments glu- 

 cose and saccharose rapidly with acid and gas production, and 

 lactose, also, when the cultivation is prolonged. Dulcite is not 

 fermented by it, and it does not produce indole in peptone solu- 

 tions; like B. aerogenes, however, it gives the Voges-Proskauer 

 reaction. 



Other organisms closely allied to B. coli are Bact. Grilnthal^ 

 Bact. neapolitanus, Bact. oxytocus perniciosus, and Bact. coscoroba. 



For the biological characters of Bact. coli and " coliform " 

 glucose-fermenting organisms, see table on p. 306. 



6. Bacterium fluorescens liquefaciens, Fliigge, is one of the 

 commonest species of bacterium in water, soil, and sewage ; it 

 also occurs in milk and other food materials sometimes, and 

 assists in the putrefaction of organic substances. It is a motile 

 organism from 1.4 to 5 a long, .4 to .5 ^ broad, with a bundle of 

 three to six polar flagella, on account of which it is occasionally 



