366 Suppuration 



the liquefaction progresses. Four or five days must elapse 

 before the medium is all fluid. 



Gelatin Punctures. In gelatin puncture cultures the 

 chief development 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 (fluorescein) 

 which soon saturates the culture-medium and gives it the 

 characteristic fluorescent appearance. As the culture ages, 

 or if the medium upon which it grows contains much pep- 

 tone, 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 Jor- 

 dan.* Its formula, according to Ledderhose, f is C 14 H 14 N 2 O. 



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

 agar, upon which much stress has recently been laid by 

 Martin, J is the formation of crystals in fresh cultures. 

 Crystal formation in cultures of other bacteria usually takes 

 place in old, partially dried agar-agar cultures, but Bacil- 

 lus pyocyaneus often produces crystals in a few days upon 

 fresh media. In my experience freshly isolated bacilli 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 fluorescence, 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 alkaline 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 



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

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

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



