EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 37 



teria may be placed upon the cover-glass by allowing the 

 glass to fall upon one of the colonies of bacteria, on a gelatin 

 or agar plate (see page 99), which will adhere to it in part, 

 producing an " impression preparation " (German, Klatsch- 

 preparat}. Such a preparation, after drying in the air, is 

 to be fixed by passing it through the flame three times. (See 

 below.) The forceps with which it is handled should be 

 sterilized in the flame. 



Generally bacteria contained in fluids, like sputum, or 

 taken from the surface of a culture, are smeared over the 

 cover-glass by means of the platinum wire or loop, which 

 must be heated to a red heat before and after the opera- 



FIG. 7. 



Cornet forceps for cover-glasses. 



tion. Such preparations are called smear, cover-glass, 

 cover-slip, or film preparations. When the material to be 

 spread is thick or very viscid, a small drop of distilled 

 water must first be placed in the center of the cover-glass 

 so as to dilute it. Beginners generally take too much ma- 

 terial on the wire. As thin a smear as possible is made. 

 It is allowed to dry in the air; this should occupy a few 

 seconds. The drying may be hastened by holding the 

 forceps with the cover-glass a long distance above the 

 flame, at a point where the heat would cause no discomfort 

 to the hand. Having dried the preparation, it is to be 

 passed through the flame of a Bunsen burner or alcohol 

 lamp three times, taking about one second for each transit. 

 The heat of the flame serves to dry the bacteria upon the 

 cover-glass and fix them permanently in position; it is not 



