I] MICROSCOPIC EXAMINATION u 



with a cover-glass. In some special instances, such as the 

 bacilli of leprosy and tuberculosis, double staining is 

 required. With other organisms, such as the bacilli of 

 glanders or tuberculosis, the washing is carried out, not 

 with water but with acid (acetic acid and nitric acid 

 respectively). All the details will be stated when dealing 

 with these special organisms. 



The method extensively and successfully used for the 

 demonstration and preservation of microscopic specimens 

 of micro-organisms in fluids, in blood, pus, mucus, and 

 juices, is that of Weigert and Koch, which consists in 

 spreading out on a glass slide or cover-glass a very thin 

 film — the thinner the better — of the fluid (artificial or 

 natural culture medium), blood, pus, or juice, and drying 

 it rapidly by holding it for ten to twenty seconds over the 

 flame of a spirit-lamp or gas-burner. The most successful 

 preparations are obtained when the heating is carried on for 

 such a time that the film, having become opaque at first, 

 rapidly turns transparent. Several drops of the aniline dye 

 to be used are then poured over the specimen, or the film 

 is placed over the dye contained in a watch-glass; and 

 after remaining in contact from half to thirty minutes or 

 more, according to the nature of the microbes and the dye, 

 the specimen is removed. 



The cover-glass specimen is then well rinsed with distilled 

 water, dried over the flame, and mounted in Canada-balsam 

 solution or Dammar varnish — of course always bearing in 

 mind on which surface of the cover-glass the film has been 

 spread. If the film has been well heated in the first 

 instance washing in water is quite sufficient, but if the 

 drying has been insufficient a good deal of diffuse staining 

 of the ground substance has taken place, and then the 

 cover-glass specimen must be also washed in alcohol 



