TEXT-BOOK OP BACTERIOLOGY. 183 



already reached the surface show a circular, sharp border, with 

 strong refractive power, which is, in fact, the line of demarcation be- 

 tween the liquefied and still solid gelatin. At the bottom of the 

 former lies the granulated mass of the colony, which already shows 

 the bluish-violet coloring matter. The further the development pro- 

 ceeds the more closely the pigment becomes visible to the naked 

 eye. 



In the test-tube this bacillus hquefies the gelatin in the shape 

 of a funnel, and throughout the whole depth of the puncture. On 

 the surface there is generally formed a bubble-like contraction, 

 while the chief mass of the culture sinks to the bottom of the 

 funnel-shaped hquefaction in small coiled-up bluish-white masses. 

 On oblique agar a deep bluish-black coating forms, which shines as 

 if lacquered. On potatoes the bacillus grows at a moderate rate 

 and forms a bluish-black covering. 



There is also a red-water bacillus. It is extremely mobile, and 

 shoots hastily across the microscopic field in long threads. Its 

 separate cells are about the same size as those of the violet bacillus. 



On the glass plate the red-water bacillus appears in small, yel-» 

 low, lumpy colonies, which soon become surrounded with a tender, 

 transparent, collar-like border. Then the liquefaction of the gelatin 

 commences, and the colony becomes an evenly-granulated mass. 

 In the test-tube the secretion of a yellowish-red coloring matter 

 occurs, together with the liquefaction of the gelatin. On the sur- 

 face a thin, somewhat crumpled skin is formed, under this is a layer 

 but slightly colored, and at the bottom the yellowish central mass 

 of the culture, consisting of slimy threads. On agar a thin cover- 

 ing spreads out, which is clearly yellow in the middle, while the 

 irregular edges are paler. 



The best field for the development of the pigment peculiar to 

 this species is the potato. Here the whole surface is quickly cov- 

 ered with a rusty-red or orange-yellow coating, which is scarcely to 

 be found elsewhere in such perfection. 



Fluorescent <B acteria. 



Several of the bacteria which occur frequently in water produce 

 on gelatin a green pigment, which under some circumstances is 

 beautifully fluorescent, and the color of which reaches far into the 

 culture medium. Two of them, differing in the forms of their col- 

 onies on the glass plate and in the appearance of the cultures in 

 test-tubes, liquefy the gelatin, and two of them develop without 

 liquefying it. 



