OF THE DIATOMACE^. 283 



will be found at the bottom of the first vessel, which may of 

 course be thrown away with every feeling of satisfaction on the 

 part of the operator. When the material in the larger beaker has 

 settled, it is poured back into the smaller one, and the foregoing 

 process repeated, the densities varying according to the time allowed 

 for their settlement, and if the patience is not quite exhausted, as 

 many as six or seven densities may be obtained, containing forms 

 varying very much from each other. 



The larger forms, as Triceratium, Coscinodiscus^ and Heliopelta^ 

 are to be found in the coarsest density, and the broken forms in 

 the Ughtest. When it is desired to preserve such forms as Dickeia 

 and Schizonema in their natural condition, I think there is no 

 better process than that of Herr Hantzsch of Dresden, the 

 advantage of whose method is, that a gradual application of the 

 preservative fluid is brought about, the action of endosmose 

 slightly retarded, and there is also a better adjustment of the 

 density within and without the vegetable cell. The fluid he 

 recommends is composed of 



3 parts Pure Alcohol, 



2 ,, Distilled Water, 



I ,, Glycerine. 

 A cell having been made of Gold size and allowed to become 

 " tacky," a drop of distilled water is laid in the centre, and in 

 this the Diatom or Diatoms are placed, and then a few drops of 

 the preservative medium added. The sHde must be laid aside 

 for awhile, and covered with a bell-glass to exclude the dust ; after 

 a short time it will be found that the glycerine alone remains, 

 more of the liquid must be added, and subsequent evaporation 

 submitted to, till the cell becomes full of glycerine. The cover- 

 glass should now be applied, a thin ring of gold size is drawn 

 round the edge of it, which will temporarily secure it, and on 

 this becoming hard, the cell is finished with gold size and varnish 

 in the usual manner. 



A somewhat new medium has been recommended by 

 that celebrated Diatomist, Dr. Von Heurck, which is a solution of 

 Styrax in benzole or chloroform ; personally I prefer the latter. 

 Mr. A. C. Cole, of London, refers to it at length in a recent 

 number of his " Popular Studies," therefore I do not think it 



