28 JOURNAL OF THE [April, 



chromate or tannin ; or, in Luffler's method, B the hot mordant, 

 and D the colorant. The covers are to be first firmly inserted in the 

 coil with the help of a knife-blade, with the films downward, and 

 so suspended from the cork. In the campechian staining method, 

 the stain in the flask is previously brought up to the boiling point 

 by holding it a few minutes over a flame. The cork is then in- 

 serted, making sure that the covers remain entirely immersed in 

 the hot stain. The apparatus is left upon a mounting-table, so 

 heated as to keep the liquid very near or just below the boiling 

 point, and there allowed to remain for the length of time desired 

 in any particular case, which may even be an hour or more. A 

 large number of covers may be thus stained at one time, with little 

 needed attention. The cork is finally lifted out of the flask, and 

 the coil, without removal of the covers, is plunged into successive 

 beakers of distilled water until the covers are thoroughly washed 

 from excess of stain. Then the glass stopper is removed from 

 the bottle and replaced by the cork, so that the coil with its 

 burden of covers now remains plunged in the mordant for the 

 requisite time. 



It may be added that the staining-flask is useful as well in many 

 cases where there is call for long and slow staining of films on 

 covers in a cold solution. The handling of thin covers in mass, 

 by this method, rather than individually, is found to diminish 

 greatly their liability to breakage. 



IV. Condensed Air- Film. 



We have next to consider a long neglected source of the air- 

 bubbles which form a constant annoyance to the working micro- 

 scopist. At times they may only indicate the content of air 

 originally dissolved in the cold preservative, expelled by warming 

 it. and likely to be entirely reabsorbed in the course of time, after 

 the cooling of the mount. Frequent instances of this occur, espe- 

 cially in the use of warmed glycerin jelly, melted Canada balsam, 

 and dammar. More commonly they may be derived from entan- 

 glement with the fibres of a filamentous object, enclosure in the 

 pores or empty cells of a cellular object, or simply from mechan- 

 ical attachment to the cell-wall or to the cover, overlooked in hasty 

 mounting without sufficient use of the pocket lens. Their neglect 

 in such instances may injure the appearance of a mount and inter- 



