100 ELEMENTS OF WATER BACTERIOLOGY 



usually motile rod, with diameter generally less than one 

 micron and exhibiting no spore formation. It often ap- 

 pears in pairs of rods so short as to suggest a diplococcus. 

 It decolorizes by the Gram stain. It forms thin, irregu- 

 lar translucent films upon the surface of gelatin, called 

 " grape-leaf colonies " by the Germans, produces 

 no liquefaction, and gives a wire-nail-like growth in 

 stick cultures. It forms a white translucent layer of 

 characteristic appearance upon agar, produces a more 

 or less abundant, moist, yellowish growth on potato, 

 and turbidity and some sediment in broth; it ferments 

 dextrose and lactose with the formation of gas of which 



the ratio is approximately, - - = - , as ordinarily deter- 



C(J2 I 



mined; a strong acid reaction and gas are produced 

 in many other sugar-containing media. The organism 

 generally gives a characteristic reaction in esculin 

 media and typically reduces neutral red, changing 

 its color to canary yellow with a greenish fluorescence. 

 It grows in the Capaldi-Proskauer media, forming 

 acid in the albumin-free medium, No. i, and giving 

 a neutral or alkaline reaction in the peptone-mannite 

 medium No. 2. It coagulates casein in litmus milk, 

 and reduces the litmus with subsequent slow return 

 of the color (red), and generally forms indol in peptone 

 solution. Many cultures of this organism are fatal 

 to guinea pigs when the latter are inoculated sub- 

 cutaneously with one-half c.c. of a 24-hour bouillon 

 culture, and most cultures produce death when this 

 amount is inoculated intraperitoneally. Although not 

 a spore-forming bacillus, and in general not possessing 



