H. MORLAND ON MOUNTING DIAT0MACE2E. 319 



about J inch wide, the internal diameter being | inch smaller 

 than the cover-glasses intended for same. I take care to have 

 plenty of cement which can all be put on in one operation ; I 

 allow these rings to dry for a day or two, during which time 

 the bulk of the solvent of the cement will evaporate, after 

 which I harden these rings off thoroughly in a cool oven, when 

 they are ready for future use. Secondly, I take care to have 

 my diatom material in clean distilled water ; if it has been put 

 up in alcohol, the alcohol must be removed as far as possible 

 and its place renewed with water. If diatoms be dried out of 

 alcohol they will do so in a very irregular manner; they cannot, 

 however, be preserved for any length of time in water, as 

 fungoid growths will eventually appear and mat the diatoms 

 together in lumps. Thirdly. I have a block of iron, three 

 inches square and two inches thick ; this I heat on a kitchen 

 range and place on some old book or other, making use of it as 

 a " hot table." Its advantages are that it is steady and that 

 the heat can be so well regulated, such heat being retained for 

 some little time ; of course, the larger the block, the longer will 

 the heat remain fairly constant. Having one or more clean 

 cover-glasses and everything else ready, I now commence 

 operations by shaking up my tube of cleaned material and, 

 before the diatoms can settle down again, taking some of the 

 same up in a pipette, the end of which has been drawn down so 

 that the aperture does not exceed y 1 ^ inch diameter at most, 

 and placing a drop of my material on each of my cover-glasses ; 

 if necessary, this drop can be spread over the whole surface of 

 cover-glass either by breathing upon it or by means of a hair 

 or bristle, but if the latter plan be adopted it is as well to 

 shake the cover-glass sideways a little and let the diatoms 

 settle evenly. If the diatoms be large a little heat may be 

 applied to dry off the water, but if small, no heat whatever 

 must be used as otherwise the diatoms will certainly dry in 

 lines and ridges. When the diatoms are dry all that is now 

 necessary to finish the mount is to place the cover-glass on the 

 hot block, turn a "ringed" slip over and press the same down 

 on to the cover, taking care that the ring and cover centre each 

 other. The heat of the hot block will soften the cement and 

 cause the cover to adhere to the same; the slip, being trans- 

 parent, allows one to see exactly what is going on underneath, 



