26 BACTERIA 



little action upon bacteria, though that which it has is similar 

 to sunlight. Recent experiments with the Rontgen rays 

 have given negative results. 



In 1890 Koch stated that tubercle bacilli were killed after 

 an exposure to direct sunlight of from a few minutes to 

 several hours. The influence of diffuse light would obviously 

 be much less. Professor Marshall Ward has experimented 

 with the resistant spores of Bacillus anthracis by growing 

 these on agar plates and exposing to sunlight. From two to 

 six hours' exposure had a germicidal effect. 



It should be remembered that several species of sea-water 

 bacteria themselves possess powers of phosphorescence. 

 Pfluger was the first to point out that it was such organisms 

 which provided the phosphorescence upon decomposing wood 

 or decaying fish. To what this light is due, whether capsule, 

 or protoplasm, or chemical product, is not yet known. The 

 only facts at present established are to the effect that certain 

 kinds of media and pabulum favour or deter phosphor- 

 escence. 



Desiccation. A later opportunity will occur for considera- 

 tion of the effect of drying upon bacteria. Here it is only 

 necessary to say that, other things being equal, drying 

 diminishes virulence and lessens growth. 



Oxygen. Pasteur was the first to lay emphasis upon the 

 effect which free air had upon micro-organisms. He classi- 

 fied them according to whether they grew in air, aerobic, or 

 whether they flourished most without it, anaerobic. Some 

 have the faculty of growing with or without the presence of 

 oxygen, and are designated as facultative aerobes or anaer- 

 obes. As regards the .cultivation of anaerobic germs, it is 

 only necessary to say here that hydrogen, nitrogen, or car- 

 bonic acid gas may be used in place of oxygen, or they may 

 be grown in a medium containing some substance which 

 will absorb the oxygen. 



Modes of Bacterial Action. In considering the specific 



