22 



THE BIOLOGY OF BACTERIA 



In one experiment the water was exposed in bottles. In this 

 case about 98 per cent, of the germs were destroyed after fifteen 

 minutes, the cultures varying somewhat. The germs persisted in 

 the water in considerable numbers for two hours and in small 

 numbers up to four hours, after five hours the sample being 

 completely sterilised. The results of this experiment are shown 

 as follows:^ 



Table showing Change in Numbers of B. coli in Water in 

 Bulk on Exposure to Sunlight. 



It has been found that the electric light has but little action upon 

 bacteria, though that which it has is similar to sunlight. Eecent 

 experiments with the Rontgen rays have not given bactericidal 

 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 the property of phosphorescence. Pfiiiger 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 

 phosphorescence. 



* See Trans. .Tenner Inst, (second series), 1899, p. 81. 



