306 BACTERIOLOGY. 



bright yellowish-green color ; but as growth is compar- 

 atively 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 lustre, and is of a whitish or greenish- 

 white 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 from ten minutes to half an 

 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 

 mycoderma is also produced. As growth progresses, 

 the bouillon becomes darker and darker in color, until 

 it finally is about comparable in this respect with crude 

 petroleum ; at the same time it assumes a peculiar ropi- 

 ness, and very old cultures (four to six weeks in the 

 incubator) may attain about the consistency of egg- 

 albumin. This is due to the production of a substance 

 closely allied, chemically speaking, to mucin. Whether 



