NOTE ON THE PREPARATION OF DIATOMS. 81 
on the slide as great a surface as possible, and to make its edges 
extend beyond the covering glass, otherwise slight traces of crys- 
tallizable matter may serve to indicate these edges, and perhaps, to 
some extent, impair the beauty of the slide—( Bull. Soc. Belge de 
Micr.) 
NOTESON THE PREPARATION OF DIATOMS: 
By E. GuiInarp. 
GREAT deal might be done to extend the study of diatoms 
if each collector were to communicate to his fellow workers 
the different fours de main that experience may have suggested to 
him. Applying this to myself I proceed to give a most easy 
method for preserving certain marine diatoms. which are generally 
found in small numbers, and are of a nature not sufficienttly sili- 
cious to withstand long boiling in acids and repeated washings 
without considerable loss to the stock. 
When good fortune has thrown in my way an alga containing 
diatoms in small quantity I employ the following method to guard 
against all chance of loss. 
The marine alga is introduced into a tube from ro to 12 centi- 
metres deep, filled three parts full with soft water, which is raised to 
boiling point just for an instant. As soon as the liquid has cooled 
the whole is well shaken—the frustules filled with their endochrome, 
‘turned green by the heat to which they have been exposed, fall to 
the bottom of the tube. ‘This first washing is replaced by another 
with distilled water, when, after standing for some hours, a decan- 
tation carefully made leaves a small deposit of diatoms of a 
greenish colour. From this deposit a minute quantity is removed 
either by means of a pencil, or better still, with the aid of a thin 
glass tube. 
Upon the cover, previously cleaned, is placed a drop of dis- 
tilled water, to which is added that portion of the deposit removed 
with the pencil. I evaporate at a gentle temperature, and then 
calcine at a whiteish red heat upon a sheet or platinum. The 
mounting is finished in the usual way, either dry or with balsam. 
I employ this method daily for the preparation of Pleurosigma 
many of the frustules of which could not stand prolonged boiling 
in acid. 
When in a botanising excursion I have gathered some specimens 
of Pleurosigma, I turn them out immediately upon my return 
into a glass of greater height than width, so as to get a thicker 
diatomiferous deposit. After standing for from 24 to 48 hours I 
pass ahair pencil several times lightly over the surface of the 
