CLEANING SLIDES AND COVER-GLASSES. 39 
‘This keeps well. Red ink (slightly diluted) will answer 
most pufposes. 
Stains should be filtered before use. Where much 
.wotk is to be done it is convenient to keep them in 
bottles which are closed with a perforated cork through 
which a small glass funnel is placed. A filter paper is 
kept permanently in this funnel, and the stain is filtered 
directly on to the slide or cover-glass. 
Gram’s iodine solution may be mentioned here, though 
it is not a ‘stain. It corisists of a solution of iodine 1 
part, iodide of potassium 2 parts, water 300 parts. 
It keeps indefinitely. 
‘CLEANING SLIDES AND COVER-GLASSES. 
Slides and .cover-glasses must be absolutely clean 
when used in the bacteriological laboratory; it is 
especially necessary that they should be free from the 
slightest trace of grease, for this will prevent: fluid from 
spreading out into a thin and uniform film. 
Slides are best cleansed by dropping them one at a 
time into strong nitric or sulphuric acid, and allowing 
them to soak for an hour or more. They are then 
washed in running water for another hour, soaked in 
strong ammonia for an hour, and kept in alcohol. As 
methylated spirit is not so good for this purpose the use 
of alcohol is rather expensive; but it is not absolutely 
necessary, and the slides may be stored in a solution of 
ammonia (about 1 in ro) until required. When about 
to be used they are to be wiped dry with an old linen 
handkerchief kept specially for the purpose. This 
handkerchief should be as old as possible, and should 
have been washed until it has begun to fall to pieces. 
