312 B A GTERIOLOG Y. 



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 

 mycoderrna 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 

 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 ; at all events, in cultures 

 presenting this peculiarity very few bacteria of normal 

 appearance indeed, very few bacteria at all are to be 

 seen on microscopic examination. 



In milk it causes an acid reaction, with coincident 

 coagulation of the casein. 



On blood-serum and egg-albumin its growth is ac- 

 companied by liquefaction. The growth on coagulated 



