94 BACTERIA less, viii 



For the most part Bacteria are unaffected by light, since 

 they grow equally well in darkness and in ordinary daylight. 

 Many of them, however, will not bear prolonged exposure to 

 direct sunlight, and it has been found possible to arrest the 

 putrefaction of an organic infusion by insolaiion, or exposure 

 to the direct action of the sun's rays. It has also been 

 proved that it is the light-rays and not the heat-rays which 

 are thus prejudicial to the life of microorganisms. 



