PSEUDOMONAS &RUGINOSA 387 



bright yellowish-green color; but as growth is comparatively 

 rapid, it is quickly entirely liquefied, and one often sees the 

 colonies floating about in the pale-green fluid. 



On agar-agar the growth is dry, sometimes with a slight 

 metallic luster, and is of a pale gray or greenish-gray color, 

 while the surrounding agar-agar is bright green. With 

 time this bright green becomes darker, passing into blue- 

 green, and finally turns almost black. 



On potato the growth is brownish, dry, and slightly 

 elevated above the surface. In some cultures the potato 

 about the line of growth becomes green; in others this 

 change is not so noticeable. With many cultures a peculiar 

 phenomenon, consisting of a change of color from brown to 

 green, may be produced by lightly touching the growth with 

 a sterile platinum needle. The change occurs only at the 

 point touched. It is best seen in cultures that have been 

 kept in the incubator for from seventy-two to ninety-six 

 hours. It occurs in from one to three minutes after touching 

 with the needle, and may last for from ten minutes to a half- 

 hour. This is the " chameleon phenomenon" of Paul Ernst. 



In bouillon the green color appears, and the growth is 

 seen in the form of delicate flocculi. A very delicate my co- 

 derma is also produced. As growth progresses, the bouillon 

 becomes darker and darker in color, and more or less fluores- 

 cent, until it finally is about comparable in this respect to 

 crude petroleum; at the same time it assumes a peculiar 

 ropiness, and very old cultures (four to six weeks in the incu- 

 bator) may attain about the consistency of raw egg-albumen. 

 This is due to the production of a substance closely allied, 

 chemically speaking, to mucin. Whether it is a metabolic 

 product or one resulting from the degeneration or the auto- 

 digestion, so to speak, of the bacteria, cannot now be said; 



