332 Suppuration 



Microscopic examination shows the superficial colonies to be 

 rounded and coarsely granular, with serrated or slightly filamentous 

 borders. They are distinctly green in the center and pale at the 

 edges. The colonies sink into the gelatin as the liquefaction pro- 

 gresses. Four or five days must elapse before the medium is all 

 fluid. 



Gelatin Punctures. — In gelatin puncture cultures the chief de- 

 velopment of the organisms occurs at the upper part of the tube, 

 where a deep saucer-shaped liquefaction forms, slowly descending 

 into the medium, and causing a beautiful fluorescence. At times a 

 delicate scum forms on the surface, sinking to the bottom as the 

 culture ages, and ultimately forming a slimy sediment. 



Agar-agar. — Upon agar-agar the growth developing all along 

 the line of inoculation at first appears bright green. The green 

 color depends upon a soluble pigment (fluorescin) which soon 

 saturates the culture-medium and gives it the characteristic floures- 

 cent appearance. As the culture ages, or if the medium upon which 

 it grows contains much peptone, a second blue pigment (pyocyanin) 

 develops, and the bright green fades to a deep blue-green, dark blue, 

 or in some cases to a deep reddish-brown color. This pigment has 

 been made the subject of a careful investigation by Jordan.* Its 

 formula, according to Ledderhose,t is C14H14N2O. 



A well-known feature of the growth upon fresh agar-agar, upon 

 which much stress has recently been laid by Martin, { is the forma- 

 tion of crystals in fresh cultures. Crystal formation in cultures of 

 other bacteria usually takes place in old, partially dried agar-agar, 

 but Bacillus pyocyaneus often produces crystals in a few days upon 

 fresh media. Freshly isolated bacilH show this power more markedly 

 than those which have been for some time part of the laboratory 

 stock of cultures and frequently transplanted. 



Bouillon. — In bouillon the organism produces a diffuse cloudiness, 

 a flourescence, and sometimes an indefinite thin pellicle on the surface. 



Potato. — Upon potato a luxuriant greenish or brownish, smeary 

 layer is produced. 



Milk.— Milk is coagulated and peptonized. It is slightly acid 

 for the first day or two, then becomes alkahne again. 



Metabolic Products.' — Apart from the pyocyanin and fluorescin, 

 the former blue, the latter green, cultures of this organism frequently 

 turn red brown. This suggested the formation of a. third pigment, 

 but the work of Boland§ has shown this to be a transformation prod- 

 uct of pyocyanin common in old cultures. 



The organism produces a curdling ferment, a fibrin- and casein- 

 dissolving ferment, a gelatin-dissolving ferment, and a bacteriolytic 



* "Journal of Experimental Medicine," 1899, vol. iv. 



t "Deutsche Zeitschr. f. Chirurgie," 1888, Bd. xxviii. , 



t "Centralbl. f. Bakt.," April 6, 1897, xxi, p. 473. 



§ "Centralbl. f. Bakt.," 1899, Bd. xxv, p. 879. 



