Invert a finger bowl or a bell glass over the cap to keep the air from blowing the spores away.
The impregnation may also be effected in rarefied air under a bell glass (p. 68).
The instrument consists of a bell glass, from the inside of which is suspended a copper needle by a fine silken thread.
In a few minutes the air will be decomposed, and nitrogen alone remain in the bell glass.
A good microscope requires its own table; and when not in use should be covered by a bell glass or a clean linen cloth.
Carry out the method as far as possible under cover of a bell glass, to avoid aerial contamination.
Remove the bell glass altogether and press the cover-slip firmly on to the cell.
Place the slide and block covered by the bell glass in the incubator at 37° C. for ten minutes to dry slightly.
When the stock has been housed in the cabinet, whatever is left may be transferred to the bell glass for further examination.
Keep closely covered with a bell glass and, in a few weeks, more or less, the baby Ferns will start to put in an appearance.