THE MICROSCOPE. 141 



ror for light, and an inch objective focussed on the perforated 

 cap. Move the condenser about until the perforation is exactly 

 in the centre of the field, then secure it. Practice with familiar 

 objects, like blood corpuscles, diatoms, etc , until the effect of 

 various openings and positions is known. Central light is the 

 rule for histological work. When using high-angled objectives, 

 as in bacteriology, make immersion contact with glycerine or 

 horn. imm. fluid between the top lens of the condenser ,and the 

 lower side of the mount. With high-angled objectives, there is 

 no such breaking-down of the images under a flood of light as 

 may be seen ordinarily with the low-angled objectives. With 

 the latter, delicate details require a dimmed light producing a 

 dim, uncertain image. With the former, a much brighter light 

 can be employed and sharp, crisp details enjoyed. 



PRACTICAL SUGGESTIONS 



By L. A. WHiLSON, CLEVELAND, OHIO. 



Mounting Cyclops. — It is desirable to mount Cyclops quad- 

 ricornis so that the egg sacs will be preserved. With patience, 

 time, and perseverance, it can be done. 



Begin by first preparing the slides with white-zinc rings. 

 Lay them away until the rings are dry and hard. When the 

 slides are thoroughly seasoned, place a Cyclops within the ring 

 and a cover glass on the ring, thus enclosing the Cyclops with a 

 ring full of water under the cover. Make a mounting fluid by 

 mixing one-half lime water and one-half glycerine. Run the 

 lime mixture under the cover at one side and soak out the orig- 

 inal water at the other side with a piece of blotting paper. The 

 reason for using lime water with the glycerine is, that the Cy- 

 clops is composed largely of carbonate of lime which pure gly- 

 cerine will dissolve and destroy. Make a white zinc ring so as 

 to fasten the cover temporarily. Set it away to dry and harden 

 and in a day or two add another ring, repeating successive ring-* 

 until a properly finished ring is made. It may take a week to 

 finish a slide properly, but prepared in this way, one cannot 

 fail to succeed. Undiluted glycerine will cause the Cyclops to 

 disappear. This method, was invented by Mr. Montague Rogers, 

 of Cleveland, and it brings this Entomostracan into a natural 

 position with horns and egg bags extended. 



