THE STAINING OF COVER-GLASS PREPARATIONS. 93 



bacteria off the cover- glass with them. Should it be 

 impossible to avoid taking a minute quantity of gela- 

 tine, etc., a little white of egg should be added to, and 

 thoroughly mixed with, the bacterium material. This 

 is often strongly to be recommended when anaerobes, 

 which grow in the interior of solid media, are to be 

 examined, although, under these circumstances, the 

 preparation never presents the same clean and pretty 

 appearance as when 'none of the medium is conveyed 

 on to the cover-glass. As concerns the quantity of 

 material which should be used for these cover-glass 

 preparations, it should be noticed in the first place 

 that the farther apart the individuals are from each 

 other, the more distinct and pretty are the prepara- 

 tions. On this account only a small quantity of bac- 

 terium material should be placed upon the cover- glass ; 

 it does not much matter how much liquid is added, 

 except that, of course, the less there is the more 

 quickly does the preparation dry. If the liquid does 

 not spread itself out evenly over the cover-glass, but 

 returns to the place where it was put, it shows that 

 the cover-glass was not quite clean, but had a minute 

 layer of grease upon it, which must be removed by 

 heating it again in the flame and polishing it with a 

 dry cloth. Care must be taken over all these details, 

 if we do not wish to have a great deal of useless labour 

 and trouble. 



When the cover-glasses have been dried in the air 



