26 



MANUAL OF BACTERIOLOGY. 



a red heat before and after the operation. 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 

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



Fig. 7. — Cornet Forceps for Cover-glasses. 



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 with the smeared surface up 

 three times through the flame of a Bunsen burner or alcohol 

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



Fig. 8. — Stewart Forceps eor Cover-glasses. 



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

 sufficient, however, when applied in this manner, to kUl all 

 kinds of bacteria, especially those containing spores. After 

 it has been passed through the flame three times the preparation 

 may be stained with a solution of one of the anihne dyes, as 

 described below, and after washing in water and drying may be 

 mounted, face down, in Canada balsam upon a glass slide. It 



