On Double and Treble Staining/. By Heneage Gibhes. 393 



I should like to impress practical microscopists with the 

 benefit to be derived from using cover-glasses of a known thick- 

 ness, and as these can now be procured at a slight advance on the 

 cost of the others, there is really no reason why they should not be 

 universally used. For a long time I only used two thicknesses, 

 •006 and 'OOi; but since I have had a ^^ made by Messrs. 

 Powell and Lealand, I have been obliged to use cover-glasses 

 thinner still. 



The great advantage of knowing the thickness of the cover- 

 glass will be at once apparent to those accustomed to use 

 glasses with a correction collar, and those glasses without it are 

 generally corrected to a cover-glass -006, so that as there are 

 comparatively few so thin as this in the glass sold as extra thin, 

 the best result is seldom obtained ; and, again, in making 

 exchanges of duplicates, how vexing it is to find that your favourite 

 glasses will not work through the cover-glass. 



VOL. III. 2 D 



