<30 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 bo 

 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 tilled with 

 what is nearest. 



From the stomachs of common fish as the cod, sole, had- 

 dock, &c. many specimens of Diatomaceae 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 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 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 



