362 THE CULTIVATION OF DIATOMS 



plan of a second thin glass in the inside of the ring, fixed to the 

 cover-glass at some hundredths of a millimetre distance (see Fig. 

 3). By this means the level of the liquid may be considerably 

 lowered and agitated with more or less force, without the risk of 

 drying or displacing the creatures that are growing between the 

 plates. 



Plan of Cultures in these Microscope Cells.— The cells, filled 

 with water and charged with a very small portion of bran, are 

 exposed for an hour in a water-bath to a temperature of 70° C, to 

 destroy all pre-existing germs of algas or infusoria. This done, 

 and the cell cooled down, you sow, by means of a pipette with a 

 point, drawn out and bent, a little of the liquid of a culture 

 already formed, and leave the cell lying on the glass cover, with 

 the glass slip uppermost. The whole is placed on a plane slighdy 

 inclined, and covered, according to its needs, with paper — white, 

 black, or coloured. The incfination of the plane or of the sus- 

 pending apparatus ought to be such that the bubble of air in the 

 cell should open to the circular aperture formed in the glass slip. 



At the end of some days the interior surface of the cover-glass 

 will be covered by a light deposit, where the Diatoms stir and 

 freely multiply in filaments if they are moveable ; or they multiply 

 in various other manners if they are immovable (Melosira, Bid- 

 dulphia, Fragillaria, Meridion, etc.). 



The liquid that evaporates from the cell is replaced with boiled 

 distilled water by means of a capillary pipette. This need only 

 be done every eight days in the heat of summer and not more than 

 once a fortnight in winter. It is well to place above the opening 

 in the glass slip a little circular bit of flannel, as much to lessen 

 the evaporation as to preserve the maceration from contact with 

 atmospheric impurities. 



You may thus cultivate, during six, eight, or even ten months, 

 the same species ; follow all the different phases, from the first 

 appearance of the Diatoms after they have been sown, to the for- 

 mation of the auxospores, and ultimately to the decay of the 

 frustules; you may also fix, by means of photography, all the 

 interesting phenomena that present themselves. I need not repeat 

 that the arrangements of my cells admit of treating the contents 

 with poisonous substances and observe their reaction, and then 



