BACTERIUM PYOCYANEUM. 283 



round disks, with border almost smooth, more or less 

 strongly granular, very often also moruloid, light yellow to 

 greenish-yellow. Except for the color, it is not distin- 

 guishable from Bact. fluorescens, putidum, and coli (24, 

 vn). (Compare also 25, vi; 26, vm. ) 



Agar Stab. Stab : Non-characteristic, thread-like, and 

 a little nodular. Surface growth : Whitish-gray to greenish, 

 dull to moistly shining. In forty-eight hours it is uni- 

 formly spread over the entire surface. The agar has a yel- 

 lowish-green to bluish-green fluorescence. 



Agar Streak. Somewhat spreading growth, with a 

 moist luster, wavy, smooth border, yellowish-green in 

 color. The agar shows marked blue to yellowish-green 

 fluorescence. The water of condensation is almost clear; 

 there is a white precipitate and a whitish pellicle on the 

 surface (24, n). 



Bouillon Culture. Marked yellowish-green fluores- 

 cence. Very turbid. Moderate quantity of sediment, 

 which is broken up with difficulty upon shaking. Pellicle 

 upon the surface. 



Milk Culture. Milk is coagulated, and later again 

 liquefied. The liquefied portion presents yellowish-green 

 fluorescence. Reaction is always alkaline. 



Potato Culture. At first a yellowish growth, with 

 a moist luster, wavy irregular border, and but slightly 

 elevated; later, brownish-yellow to brown or reddish- 

 brown. Often there is a fluorescent zone about the growth 

 (24, vm). According to the character of the potato, 

 there is very great variation in the luxuriance, fluores- 

 cence, and color, and so the growth cannot be distin- 

 guished at any time with certainty from that of other 

 fluorescent varieties. (See also 25, ix. ) 



Sensitiveness to Injurious Agencies. Drying kills 

 rapidly. The action of the sun's rays for four hours does 

 not entirely suspend chromogenesis. 



Chemical Activities. 



(a) Chromogenesis: In its typical cultures the Bact. pyocyaneum 

 forms two pigments: a green-yellow, fluorescent bacteriofluorescein, 

 soluble in water, and the beautiful blue, crystalline pyocyanin, soluble 

 in chloroform (see p. 68). There are cultures, however, like the one 

 represented in our plate, which produce scarcely any pyocyanin, only 

 much" bacteriofluorescein. We have often seen cultures which form 



