34 PREPARATION AND MOUNTING 



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, haddock, 

 &c. many specimens of Diatomacea3 may be obtained, but 

 especially from the crab, oyster, mussel, and other shellfish. 

 Professor Smith states that from these curious receptacles 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 Diatomacese 

 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 also are now pre- 

 pared in this way, as opaque objects to be examined with the 

 lieberkuhn, and are exquisitely beautiful. Others, however, are 

 almost invariably mounted in balsam ; but as these will be again 

 referred to in Chapter III., 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 diatoms upon it. This may be held over the flame of 

 the spirit-lamp until all the surrounding matter is burnt away, 

 and a tolerable idea may be thus obtained as to the quality of our 

 treasure. 



In some cases it is well to use this burning operation alone in 

 mounting specimens of diatoms, when they may be placed in their 



