STAINING AND MOUNTING 37 



itself touch the film or cover-glass. The cover- 

 glass will not fall off the jelly, nor the jelly fall 

 off the slide, but the fumes will slowly pass in 

 between the cover-glass and jelly, fixing the cells 

 in their progress. The whole preparation may be 

 covered with the lid of a cardboard box and 

 allowed to remain for three-quarters of an hour. 1 



Removing the Cover-glass without Disturbing the 

 Cells. The slide is removed from the watch-glass 

 and laid on the table, film and cover-glass upper- 

 most. A few drops of ethyl chloride (such as is 

 used to produce anaesthesia by freezing) are 

 flooded on to the cover-glass, and then by breathing 

 on to the slide for a few moments the cover-glass 

 suddenly becomes encrusted with ice. When this 

 happens the jelly film on which the cover-glass 

 is resting contracts away from the edges of the 

 latter. With a pair of sharp-pointed forceps the 

 cover-glass is quickly seized and lifted bodily off 

 the jelly film with most of the cells fixed and 

 frozen on to it in situ. It may then be laid on 

 the bench, cells uppermost, until dry. 



Staining and Mounting. The cover-glass is 

 placed in lion-forceps and the cells stained by 

 Jenner's, Giemsa's, or other dyes as convenient. 

 I have found Jenner's stain to be very suitable. 

 After staining it may be mounted in Canada 

 Balsam, and the film can be kept as a permanent 

 specimen. 



If the cover-glass is held up to the light it 

 will be seen that a ring is formed near its 

 centre. This is the limit of fixed cells ; they are 



1 Formalin vapour can be used instead of osmic acid, but it has not 

 the same penetrating power, and the results are not so satisfactory. 

 3* 



