1900] CHROMOGENIC BACTERIA 389 
it a red dichroism makes its appearance; that is to say, the 
liquefied gelatin when viewed by reflected light is a pure grass- 
green ; when viewed by transmitted light, red. The liquefied gel- 
atin at this time cannot be distinguished in appearance from an 
alcoholic solution of chlorophyll. Like the latter it loses all its 
green tint by lamp, or ordinary gaslight (yellow light). That 
the coloring matter is, nevertheless, not chlorophyll will be seen 
from its absorption spectrum and from its behavior toward 
reagents. 
The liquefaction of the gelatin starts at the center of the 
flask, where, owing to the slight convexity of the bottom, the 
layer of the medium is thinnest. The entire medium is soon 
completely liquefied, but still retains its intense green color. 
Gradually, however, the green changes to an olive tint and then 
fades away, as does also the dichroism, leaving a brownish-yel- 
low turbid liquid. 
In order to test the green coloring matter with reagents or to 
examine it spectroscopically, a perfectly clear solution must be 
obtained. This is effected by filtering the culture medium 
through one of the bacterial filters mentioned above. When 
liquefaction has not yet taken place, sufficient water is added to 
permit its passage through the filter tubes. When liquefaction is 
advanced, filtration is at once resorted to. The first runnings 
are rejected owing to changes in color, the result of chemical 
_ action in the pores of the filter. 5 
The green non-dichroic solutions from young cultures give no 
absorption band in the neighborhood of the D line, or only the 
trace of one. The addition of a little acid produces a slight 
dichroism and a faint band appears. Acids added to any of the 
§reen dichroic solutions produce a red when in excess. cet canta 
nium hydroxid gives also a somewhat similar color. Fixed 
alkalies destroy the dichroism and yield a fine clear-green soon 
fading away. Shaking with air restores the color. These green 
alkaline solutions resemble the green ones obtained from young 
cultures and from potatoes in that they do not give an absorp- 
ion band near D. The green pigment is insoluble in alcohol 
