90 PREPARATION AND MOUNTING 



Deane's gelatine in a deeper cell ; and such a preparation is a very 

 beautiful object for the black-ground illumination. If, on the 

 other hand, the minute structure of the siliceous envelopes is the 

 feature to be brought into view, the fresh diatoms must be boiled 

 in nitric or hydrochloric acid " (which process is fully described 

 in Chapter II.). It is very convenient to have many of these ob- 

 jects mounted by two or more of the above methods ; and if they 

 are to be studied, this is indispensable. Mr. Hepworth once 

 showed me about one hundred slides which he had mounted in 

 various ways, for no other purpose than the study of the fly's 

 foot. 



My friend, Mr. Rylands, successfully mounts the diatoms in the 

 state in which he finds them, and gave me the following method 

 as that which he always employs. He says that he has had no 

 failures, and hitherto has found his specimens unchanged. Take 

 a shallow ring cell of asphalt or black varnish (which must be at 

 least three weeks old), and on the cell, whilst revolving, add a 

 ring of benzole and gold-size mixed in equal proportions. In a 

 minute or two pure distilled water is put in the cell until the sur- 

 face is slightly convex. The object having been already floated 

 on to the cover (the vessel used for this purpose being an ordinary 

 indian-ink palette), is now inverted and laid carefully upon the 

 water in the cell. By these means the object may be laid down 

 without being removed. The superfluous moisture must not be 

 ejected by pressure, but a wetted camel-hair pencil, the size made 

 in an ordinary quill, being partially dried by drawing through the 

 lips, must be used repeatedly to absorb it, which the pencil will 

 draw by capillary attraction as it is very slowly turned round. 

 When the cover comes in contact with the benzole and gold-size 

 ring, there is no longer any fear of the object being removed, and 

 a slight pressure with the end of the cedar stick of the pencil will 

 render the adhesion complete, and cement the cover closely and 

 firmly to the cell. When dry, an outer ring of asphalt makes the 

 mounting neat and complete. 



The Fungi have been before mentioned ; but it may be here 

 stated that some few of the minute forms are best preserved in a 

 very shallow cell of liquid. For this purpose creasote-water may 

 be advantageously used. 



