360 On the DiatomacecB. [Sess. 



Preservation. 



Having got the diatoms home, the next step is their pre- 

 paration for examination under the microscope, and a great 

 deal depends on the manner in which this is carried out 

 whether the examination will give real pleasure or not. It 

 will be advisable to mount some of the diatoms in their 

 natural state on the ordinary microscopic glass-slides in cells. 

 A cell of sufficient depth and size is made, and when thor- 

 oughly dry it is filled with some preservative fluid. As good 

 a fluid as any for this purpose is distilled water to which has 

 been added a trace of carbolic acid — one part of acid to a 

 hundred of water. Good specimens of the diatom or gather- 

 ing to be preserved are chosen and placed in the cell and 

 suitably arranged, if necessary, under the mounting micro- 

 scope. Before sealing up the cell, it is well to allow it to 

 remain for a day or two securely protected from dust under a 

 small bell-glass, so that any bubbles of air may escape. When 

 about to seal the cell, it must be seen that it is full of the 

 fluid, and, if necessary, a drop or so must be added. A cover 

 of thin glass of the requisite size, and thoroughly clean, is 

 taken up in the forceps ; its underside is gently breathed upon, 

 so as to cover it with a film of moisture : its edge is then 

 rested upon one of the sides of the cell, and the cover is 

 lowered gently, and in such a manner as to drive a small 

 wave of the fluid before it. If this is carefully performed, no 

 air-bubbles should be enclosed, and the cell is ready to be 

 sealed up, which is done by running several layers of cement 

 round the edge of the cover-glass and top of the cell. The 

 mount is then labelled and put past till dry. 



Cleaning. 



To see the valves of a diatom in all their beauty, they must 

 be cleansed from all adherent matter of every kind. This is 

 called the process of cleaning : it is slow and tedious, and 

 demands great care and patience on the part of the operator. 

 The order of procedure depends upon the nature of the 

 material to be cleaned. I shall take one or two typical cases 

 and treat them at some length. 





