BACTERIUM PYOCYANEVM. 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, 

 VII ). (Compare also 25, vi; 26, viii. ) 



Agar Stab. — Stab : Non-characteristic, thread-lilce, 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, ii). 



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, viii). 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 tjrpical cultures the Bact. pyocyaneum 

 forms two pigments: a green-yellow, fliaoreisoent 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 



