364 On the Diatomacecs. [Sess. 



well-corked phials of distilled water to which a small quantity 

 of alcohol has been added to prevent confervoid growths. It 

 is recommended in text-books to use distilled water in all the 

 processes. I have found well-filtered boiled water sufficient. 



Mounting. 



To have diatoms preserved in a permanent way so that 

 they can always be readily examined under the microscope, 

 they must be mounted. This is generally done on the usual 

 microscope glass-slides, 3 inches by 1 inch being the English 

 size. The diatoms should, however, be fixed on the under- 

 side of the thin glass, known as the cover-glass. There are 

 two processes of mounting — mounting dry, and mounting in 

 one or other of the different media, and here I am speaking 

 of what are called spread mounts. 



Dry Mounting. — The preliminary steps in dry mounting 

 and mounting in a medium are the same. If the diatoms 

 have been preserved in alcohol and water, it is advisable to 

 put them in a test tube and wash away all the alcohol with 

 distilled water. Having thoroughly cleaned your cover-glass 

 — circular cover-glasses are the most convenient for this 

 purpose — lay it upon your small mounting plate, and cover 

 it with a bell-glass to keep off the dust. It saves trouble to 

 arrange to make several mounts at the same time. A pipette 

 must now be used. A very convenient form is a glass tube 

 about eight inches or so in length and five millimetres in 

 internal diameter drawn to a point. The diatoms in the test 

 tube are well shaken, and a sufficient quantity taken up in 

 the pipette. By putting the finger upon the top of it, the 

 diatoms are retained, and the flow from the point can be 

 easily regulated by the partial withdrawal of the finger. The 

 cover-class is now breathed upon, and a quantity of diatoms 

 sufficient to spread over it is allowed to flow from the pipette. 

 The process is repeated till all the cover-glasses are filled. 

 They are now put aside under the bell-glass till the water 

 evaporates and the diatoms are left dry upon the glass. The 

 drying may be hastened by placing a spirit lamp with a small 

 flame under the mounting-plate on which the cover-glasses 

 have been arranged. If diatoms of different gatherings are 



