516 APPLICATION OF METHODS OF BACTERIOLOGY 



after the organism has been kept under conditions of con- 

 tinuous saprophytic growth, the colonies may be thicker, 

 denser, moister, and less translucent, but always suggesting 

 the peculiar, leaf-like contour characteristic of the colonies 

 of the colon-typhoid group under similar conditions. In 

 gelatin stab-cultures there is growth along the track made 

 by the needle, and little tendency to lateral development 

 over the surface. 



On potato, its growth may be so limited as to be scarcely 

 visible, or it may appear as a moderately voluminous gray- 

 ish-brown or light-brown layer along the track made by 

 the needle, and spreading laterally beyond this. Between 

 these extremes all gradations may be seen according to 

 the suitability of the potato used. 



In bouillon it causes uniform clouding and a more or less 

 dense sediment. It does not form a pellicle. 



Growth on blood-serum is not accompanied by liquefac- 

 tion (digestion). 



Glycerin-agar-agar appears less suited to its growth than 

 plain nutrient agar-agar. 



It does not ferment either glucose, saccharose, or lactose, 

 with liberation of gas; although in glucose media there is 

 a slight increase of acidity. 



When grown in litmus-milk, the latter, after twenty-four 

 to seventy-two hours at, body-temperature, becomes a pale 

 lilac. Later on — i. e., after six to eight days — there is a 

 development of alkali, and the lilac tint gives way to a 

 deep, distinct blue color. Coagulation is never observed. 



It is either incapable of producing indol, or has this 

 faculty developed to so limited a degree as to make the 

 matter doubtful. 



When mixed with blood-serum of individuals suffering 



