48 . BACTERIOLOGY. 



(B) COVER-GLASS-PREPARATIONS. 



The method next to be described is the most 

 commonly employed ; in addition to its value as 

 a means of examining liquids, etc., it affords the 

 additional advantage of enabling one to make, 

 if necessary, a large number of preparations which 

 when dried can be preserved, stained or unstained, 

 in ordinary cover-glass boxes ; they are then in 

 a convenient form for transport, and can be 

 mounted permanently at leisure. 



The method is as follows : A cover-glass is 

 smeared with the cut surface of an organ, or 

 pathological growth, or with sputum ; or a drop 

 of blood, pus, or other fluid to be examined, is 

 conveyed to it with a large ose. By means of 

 another cover-glass, the juice, or fluid, is squeezed 

 out between them into a thin layer, and on sliding 

 them apart each cover-glass bears on one side a 

 thin film of the material to be examined. They 

 are then placed with the prepared side upwards and 

 allowed to dry. After a few minutes, they are 

 held with a pair of flat-bladed or spring forceps, 

 with the prepared side uppermost, and passed 

 rapidly three times through the flame of a spirit 

 lamp or Bunsen burner. To stain them, put two 

 or three drops of an aqueous solution of fuchsine 

 or methyl violet over the film, and after a minute 

 or two wash off the surplus stain with distilled 

 water by means of the siphon apparatus or a wash 



