60 PREPARATION AND MOUNTING 
very useful, and one is now made with a covering upon the 
broader portion of it to protect the enclosed matter from 
being so readily carried off whilst bringing it to the surface ~ 
again. Where there is any depth of water, and the spoon 
will not reach the surface of the mud, the bottle must be 
united to a long rod, and being then carried through the 
upper portion with the mouth downwards, no water will be 
received into it; but on reaching the spot required, the 
bottle-mouth may be turned up, and thus become filled with 
what is nearest. 
From the stomachs of common fish—as the cod, sole, had- 
dock, &c.—many specimens of Diatomacez may be obtained, 
but especially from the crab, oyster, mussel, and other shell- 
fish. Professor Smith states that from these curious recep- 
tacles he has taken some with which he has not elsewhere 
met. ‘To remove them from any of the small shell-fish, it is 
necessary to take the fish or stomach from the shell, and 
immerse it in strong hot acid (nitric is the best) until the 
animal matter is dissolved, when the residue must be 
washed and treated as the ordinary Diatomacez hereinafter 
described. 
Many diatoms are seen best when mounted in a dry 
state, the minute markings becoming much more indistinct 
if immersed in liquid or balsam; and for this reason those 
which are used as test objects are usually mounted dry. 
Many kinds are also now prepared in this way as opaque 
objects, to be examined with the lieberkuhn, and are ex- 
quisitely beautiful. Others, however, are almost invariably 
mounted in balsam; but as these will be again referred to 
in Chapter IV., and require the same treatment to fit them 
for the slide, it will not be out of place to describe the 
cleaning and preparation of them here. As before stated, 
there is much matter surrounding them which must be 
got rid of before the siliceous covering can be shown 
perfectly. As, however, we may first wish to become 
acquainted in some degree with what we have to do, it is 
well to take a small piece of talc, and place a few of the 
