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are to be found in immense quantities along with the attached 

 forms, as Cocconeis, &c., and this most commonly on rocky coasts, 

 where often the algoe, rocks and coralline zoo[)hytes are covered 

 with them. Dr. Wallich found Coscinodisci, Rhizosolenice, and 

 Chcetoceras, floating on the surface of the ocean in the tropics, 

 but I have never heard of such an. occurrence in our seas. The 

 species attached to alga? may be preserved, until they are wanted 

 to be permanently mounted, in alcohol ; they are thus kept in 

 their natural state. Species may be removed from the alga) by 

 immersion and boiling in a weak mixture of nitric acid and water, 

 (containing four to five per cent, of acid,) which corrodes the cuti- 

 cle of the alga without breaking up the chains of Diatoms. The 

 alg£e may then be taken out with a glass rod, or strained off 

 through a piece of wire gauze or fine muslin ; if the latter be 

 used, the filamentous Diatoms will often be retained along with 

 the algas, and such attached species as Cocconeis pass through. 

 All marine, or brackish, species should be washed in filtered 

 freshwater, so as to remove all soluble salts, which would other- 

 wise obscure the specimens, previous to immersion in alcohol, or 

 mounting. I should mention here, that often freshwater, unless 

 it be distilled, will contain certain salts, as lime, which will, on 

 evaporation, crystallize on the glass and mar the beauty of the 

 specimen, therefore it is advisable to use distilled water, or alco- 

 hol, for the last washing. As a rule, it is always preferable to 

 make the collection as clean as possible in the first place, as it 

 will be found difiicult in many cases to render the Diatoms per- 

 fectly free from sand and mud afterward. Where they float on 

 the surface of the water, or are attached to larger alg^e, this is not 

 difficult, but where they are on the mud at the bottom it is not so 

 easy. It can, however, be done by carefully removing them with 

 a camel's-hair pencil, or, if we do not happen to have one with us, 

 the mud can be removed in a wide-mouthed bottle (selecting as 

 much of the surface as possible) and, at home, transferred to a 

 saucer and placed in the sunlight. The living specimens will 

 then congregate toward the lightest side, and may be taken up 

 with a camel's-hair pencil and transferred to a test tube or speci- 

 men vial. The latter are the vials used to hold homoeopathic 

 medicines, and those of about a drachm capacity will be found the 

 most convenient, though, for scarce gatherings, much smaller ones 



