26 BACTERIOLOGY FOR NURSES 



growth, the two being mixed and spread evenly 

 upon the glass. This film is allowed to dry in 

 the air and is then passed through the flame of 

 a spirit lamp or Bunsen burner three or four times 

 to fix the film, which is then covered with the stain 

 and allowed to stand twenty or thirty seconds, fol- 

 lowed by washing in clear water, when it may be 

 observed with a microscope, and different kinds of 

 bacteria are often easily recognized even by very 

 inexperienced observers. This is a bare outline of 

 how bacteria are stained, the method being greatly 

 elaborated for different species and conditions. 



The microscope is an indispensable adjunct to 

 work in the laboratory, the use of which requires 

 practice and delicate care. 



Animal Inoculation. Animal inoculations are 

 employed to observe the virulence of bacteria, to 

 secure pure cultures, and for continuing the life of 

 such organisms as cannot be grown outside of the 

 animal body, such as the virus of smallpox and 

 hydrophobia. 



Rabbits, guinea pigs, white rats, and white mice 

 are most commonly used. 



