CLEANING SLIDES AND COVER-GLASSES. 39 



This keeps well. Red ink (slightly diluted) will answer 

 most purposes. 



Stains should be filtered before use. Where much 

 work 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 consists of a solution of iodine i 

 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 i in 10) 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. 



