Il6 MANUAL OF BACTERIOLOGY. 



growth of some bacteria, aerobes. Its absence is equally in- 

 dispensable to certain others, anaerobes. Others still are able 

 to flourish either in the presence or absence of oxygen, facul- 

 tative aerobes or anaerobes.. The first-named varieties are 

 sometimes called strict, or obligate aerobes or anaerobes. 



Effects of Sunlight.^ — Direct sunlight kills the vegetative 

 forms of bacteria more or less rapidly, and constitutes one of the 

 most efficient among the natural methods of disinfection. 

 Diffuse daylight acts much more slowly. Electric light acts 

 like sunlight or dayhght, the results being dependent on the 

 intensity of the light. The violet part of the spectrum is most 

 active. 



The influence of electricity upon bacteria has not yet been 

 fully studied. Apparently the destruction of bacteria reported 

 as having been effected by electricity was the result of electrol- 

 ysis of the medium. 



It appears probable that X-rays do not produce important 

 effects on bacteria, although further investigation of this subject 

 is needed. The rays emitted by radium also require further 

 study. Several observers report that radium rays have some 

 germicidal power. The success which has attended the use of 

 light rays. X-rays and radium rays, in the treatment of lupus 

 and other diseases, is not necessarily to be explained as the 

 result of bactericidal action of the rays. 



