OF MICROSCOPIC OBJECTS. 69 
copic objects, but as instructive specimens. It is not, 
therefore, sufficient to take a single slide as all that is 
required, but to have the same diatom prepared in as many 
ways as possible. The following are the principal :— 
1. Mounted crude in fluid (see Chapter V.) 
2. Burnt crude upon the cover, and mounted dry or in 
balsam. 
3. Mounted dry or in balsam (see Chapter IV.), after 
the cleansing process already described. 
I will here give Mr. Rylands’ method of mounting them 
dry, the fluid and balsam preparations being noticed in 
their respective chapters. The slide, with the ring of 
asphalt, or black varnish, should have been prepared some 
weeks previously, in order to allow it to dry thoroughly. 
When required, it must be held over the spirit-lamp or 
Bunsen’s burner until the ring of varnish is softened. The 
burnt cover, having been heated at the same time, must 
then be taken in the forceps and pressed upon the softened 
varnish until it adhere all round. When cold, an outer 
ring of asphalt completes the slide. 
Such is the method which my friend Mr. T. G. Rylands 
employs in the preparation of diatoms for the microscope. 
I have said enough concerning his results. It is to be 
feared, however, that to some these several modes of opera- 
tion may appear lengthy and complicated; but if read 
earefully, and the experiments tried, they will be found to 
be simple enough in practice, and to occupy much less time 
than an intelligible description would lead the novice to 
believe necessary, 
The minute nature of diatom forms, and the high micros- 
copic powers by which they are examined, render a very 
shallow cell necessary when they are mounted upon a dry 
slide. Many early attempts, on this account, have been 
ruined by the cement used to fix the thin cover spreading 
underneath. A correspondent of the ‘ Monthly Microscopic 
Journal” thus gives his mode of avoiding this :—“ There is 
avery simple means of avoiding this danger, and I will 
