102 



METHODS OF OBSERVING BACTERIA 



Lamps. The next utensil required is a small alcohol lamp or 

 Bunsen gas burner. One or the other is necessary for sterilizing 

 the-platinum rod, which is never used unless it has previously been 

 heated in a flame and never put aside until it has gone through 

 the same process. This is the only way to avoid contamination of 

 preparations made with -outside microorganisms with which the 

 platinum loop has come in contact while in use. 



FIG. 49 



FIG. 50 



Bunsen burners. 



Glassware. The dyes used in staining cover-glass preparations 

 are best kept in small bottles provided with droppers. Aside from 

 these, small dishes are needed in which the cover-glass preparations 

 can be washed in water or alcohol. Small beakers or whiskey 

 glasses will do for this purpose. To complete the outfit for elementary 

 work, some small funnels, small round filters, and filter paper are 

 necessary, as it is sometimes desirable to filter the stain directly 

 before use on the cover-glass. A Canada-balsam bottle and somfc 



FIG. 51 



FIG. 52 



Canada-balsam bottle. 



Three staining solution bottles with droppers. 



so-called concave slides are also needed. The latter are slides 

 generally a little thicker than ordinary slides, with one or two 

 concavities ground in the glass, and used in making hanging-drop 

 preparations in studying live bacteria. 



Method of Preparing a Hanging Drop or Moist Chamber or Concave 

 Slide. The following are the steps in preparing a hanging drop for 

 studying bacteria and other microorganisms unstained and in the 

 live state: 



