540 SUMMARY OF CURRENT RESEARCHES RELATING TO 



place by simply toucting the wax with the point of a hot wire. If the 

 object is like globular sand or Polycystina, liable to roll about, a 

 depression can be turned in the central part with slight containing 



Fig. ]32. 



Central portion levelled off, also 

 part over ring fnr cover. 



walls. (Fig. 133, «, &, c.) If desired the central portion can be made 

 as high as the outside, so that the cover will touch it when in place (c). 

 If more room is needed, the whole cell may be made as at d. 



I put the cover on as follows : Heat it enough to drive off all 

 moisture, but not hot enough to melt the wax ; lay it on the cell — 

 retain it with a spring clip of sliglit pressure, and then hold it over 

 the top of a lighted kerosene lamp just an instant. The pressure 

 of the clip forces the cover into the melted wax and the cell is 

 hermetically sealed. 



Trim off on the turntable any surplus wax on the cover of the out- 

 side of the cell, and clean with a bit of cloth folded over the end of a 

 small wedge-shaped piece of wood and dipped in alcohol. 



Coat the cells and outer edge of the covers with Walmsley's zinc 

 cement ^rs/, and put on black or coloured rings after it is dry. Cells 

 that " run in " — at least, some of them — have had the Brunswick black 

 put on first. This is wrong, for the turpentine is very penetrating, 

 and should not be used until the zinc cement is quite dry. 



This method gives all the beauty and mechanical perfection of 

 lathe-work, and if due precaution is had in regard to the essential steps, 

 will give, I believe, the best cell for opaque mounting." 



Gutta-percha Cells.*— Dr. Phin has no faith in the durability of 

 gutta-percha. Every specimen that he has had an opportunity of 

 watching has become granular and brittle after a time. The finishing 

 ring of cement which Professor Smith regards as unnecessary ,■]■ he 

 considers the salvation of the cells,, The gutta-percha ring, if unpro- 

 tected, will, after a time, become a mere mass of loosely adherent 

 grains. If, however, these grains be held together with shellac or 

 some other varnish or cement, the cell may last a long time. 



Apertures in Opaque Mountings. J — Mr. C. C. Merriman recom- 

 mends that a small opening should be left into the cells of opaque 

 mountings, and gives the following directions for making it. 



* Amer. Journ. Micr., v. (1880) p. 229. 

 t See this Jonrnal. iii. (1880) p. 863. 

 ; Amer. Journ. Micr., v. (1880) p. 2.53. 



