VITAL ACTIVITIES OF BACTERIA 143 



cyaneus with chloroform, and separated from the bacterio- 

 fluorescein. 



Phosphorescent bacteria. Certain bacteria have the 

 property of emitting light when grown on solid culture media. 

 These organisms are quite widely distributed in sea-water and 

 are observed in salt fish. They have been frequently isolated 

 and studied. The giving off of light is a property of living 

 bacteria. It is not usually due to oxidation of any photogenic 

 substances eliminated by them, although such a substance has 

 been reported. Agents which are injurious to the life of the 

 bacteria affect this property. A filtrate of the cultures has 

 proven to be non-phosphorescent. Phosphorescent bacteria 

 are best grown with free access of oxygen in a culture medium 

 prepared by boiling fish in sea-water (or water containing 3 

 per cent sea-salt), to which 1 per cent peptone, 1 per cent 

 glycerin, and 0.5 per cent asparagin are added. Even in this 

 medium the power of emitting light is soon lost unless the 

 organisms are frequently transplanted to fresh media. 



Chemotaxis. This is the attraction or repulsion of bac- 

 teria by chemical substances and was first described by Strahl 

 and Pheiffer. Some chemical substances seem to exert a 

 peculiar attraction for bacteria. The bacterial proteins are, 

 according to Buchner, especially active in this respect. Other 

 chemical substances repel them (negative chemotaxis). 

 Moreover all species are not affected alike, for the same sub- 

 stance may attract some bacteria and repel others. Oxygen, 

 for example, attracts aerobic and repels anaerobic bacteria, 

 and for each variety there is a definite proportion of oxygen 

 which most strongly attracts. The chemotactic properties of 

 substances are tested by pushing the open end of a fine capil- 

 lary tube, filled with the substance to be tested, into the edge 

 of a drop of culture fluid containing bacteria and examining 

 the hanging drop under the microscope. In this way one can 

 observe whether the bacteria crowd about the tube opening or 

 are repelled from it. Peptone and urea show positive chemo- 

 taxis for nearly all bacteria, while alcohol and many of the 

 metallic salts possess a negative chemotaxis. 



