242 



OUTLINES OF BACTERIOLOGY. 



well in sewage. On the average there are 100,000 individuals of this 

 species in one c.c. of sewage. The individuals are rod-shaped, short, 

 and with well-rounded ends. They measure 2 jj. to 3 // in length and 

 0-5 /x to 0-6 ft in breadth, and are normally motile. The prevalence 

 of this species in sewage, and the ease with which it can be isolated, 

 are often taken advantage of, when it is desired to prove that a 

 certain water had become contaminated with sewage. 



Although Bac. coli communis closely resembles Bac. typhosus in 

 general characteristics, recent research has now rendered it easy to 

 distinguish these organisms. The best points of distinction can be 

 tabulated as follows : 



BAC. TYPHOSUS. 

 Rods unequal length. 



Morphology. 



Growth on gelatine and 



agar plates. 

 Gelatine culture. 

 Milk culture. 



Bouillon culture. 

 Bouillon containing lac- 

 tose. 



Neutral red-glucose agar. 

 Potato culture. 



BAC. COLI. 



Rods shorter and thicker. 

 Slow growth ; colonies Rapid growth ; colonies 



slightly raised. 

 No gas. 



well raised and larger. 

 Abundant gas. 



Not curdled ; no acid Curdled ; acid reaction. 



reaction. 



Indol not present. Indol present. 



No gas. Gas. 



No change. 

 "Invisible" growth if 



potato has acid re- 



action. 



Green fluorescence. 

 Thick yellow-white 

 growth. 



Iii addition to these, there are other tests, dependent on differences 

 of growth in various media, e.g. Eisner's iodised potato gelatine, 

 M'Conkey's lactose agar, and Proskauer &" Capalcli's medium. It must 

 be remembered that Bac. coli communis is the name rather of a group 

 of closely-allied organisms than of one species, and the above tabulated 

 characteristics refer to what may be called the central species. There 

 are at least sixteen varieties, all of which agree in being non-sporing 

 and non-liquefying ; in coagulating and producing acid in milk ; in 

 producing acid and gas in glucose and lactose media; in producing 

 acid and gas in bile-salt-glucose broth ; in growing well at 42 C. 

 Further, there are other closely-allied organisms which differ from this 

 central species only in some points. These have been collected into 

 five groups : 



Group A. Ferments lactose ; coag. milk ; no indol reaction. 



B. ,, not coag. milk ; gives indol reaction. 



,, C. ,, no indol reaction. 



D. Do .not ferment lactose ; coag. milk ; no indol reaction. 

 E. not coag. milk ; no indol reaction. 



