STAINING OF BACTERIA. 151 



hastened by waving the cover-glass over a Hame. A drop 

 of Canada balsam is then placed on the center of a clean 

 slide and the thoroughly dried cover-glass is inverted and 

 brought down on the balsam, with the specimen side turned 

 down. On gentle pressure, aided by slight heating of the 

 slide, if need be, the balsam will spread out evenly under 

 the cover-glass. If the cover-glass has not been properly 

 dried, the specimen will be hazy, and may even show drop- 

 lets of water. In either case, the stain will rapidly fade. 



The entire process of simple staining can be briefly 

 summarized as follows: 



Clean cover-glass. 



Spread specimen. 



Dry in air. 



Fix in flame. 



Add drop of water. 



Add dilute dye (i - i minute). 



Wash in water. 



Examine in water. 



Dry in air. 



Mount in balsam. 



Laboratory work. — The student should practice staining cover-glass 

 preparations made from the different potato cultures (p. 170). The sev- 

 eral dyes mentioned above should be employed. An early mastery of 

 this truly simple process of staining will save much time during the 

 subsequent work. Preparations should also be made from the white 

 matter on the teeth, near the edge of the gums, and these should be 

 examined for micrococci and bacilli, and especially for " comma 

 bacilli," spirals, and leptothrix threads. 



