142 THE MICROSCOPE. 



From March until September, the Cyclops appear in great 

 numbers in Lake Erie, and are plainly visible to the unassisted 

 eye, so that one can pick them out with a spoon, or with a dip- 

 ping tube. From a glass full of Lake Erie filterings, which can 

 be replenished weekly, one can always secure specimens. 



The Pollinia of Milkweed. — These pollen masses of the 

 milk-weed or silk-weed make beautiful slides. Under illumina- 

 tion from the mirror, they resemble plates of gold. Remove 

 the pollinia from the stamens with a needle and place them on 

 a slide. A few minutes practice will make one expert. Mount 

 at once with benzole balsam. 



Spiral Cells of the Castor Oil Plant. — The spiral cells of 

 this plant can be easily obtained and mounted. Take one of 

 the dry stems, after the plant has withered in the fall. The 

 long perpendicular fibres which may be readily stripped out 

 from the inner side are the spiral fibres. Strip out a sufficient 

 quantity to make a slide and trim them ; then stain with car- 

 mine, or other suitable stain, and clear with alcohol. Let them 

 dry on the slide and mount in balsam. The fibres will curl up 

 and appear as a lot of beautiful ringlets. 



White Zinc Mounting. — Very perfect mounts may be 

 made with white zinc. Procure a tube of white zinc from a 

 dealer in painters' supplies, and from the same source obtain a 

 bottle of prepared linseed oil. Mix a sufficient quantity of the 

 zinc and oil to make the number of slides you desire, and pre- 

 pare it as if for painting. When well mixed, and of a proper 

 consistency to flow readily, run rings on the slides with a fine 

 brush. Then, with a knife point perfect the rings on the turn 

 table. Set the slides away to dry ; keep them flat, and free 

 from dust. A dry mount may be made with one of these cells 

 by placing the cover on the hardened ring and cementing it by 

 heating a plain slide and placing it over the ring until a nar- 

 row margin runs under the cover. Then run any suitable out- 

 side ring. A ring prepared as above and thoroughly dried and 

 hardened will hold glycerine many years. To use with glycer- 

 ine, fill the cell, put the cover on, and then run a slight ring of 

 white zinc. Set it away to dry. The next day run another 

 ring. Dry it 24 hours, and so on, until the outer ring is good. 



Finish these outer rings at the time of putting them on, by 

 running them upon the turn table with the point of a penknife. 



