670 



SUMMARY OF CUREENT RESEARCHES RELATING TO 



cell, and enable the observer to remove or replenish the fluid. The 

 advantages claimed for it are the facility with which it can be used and 

 cleaned ; its reversibility, allowing either side of the object to be ex- 

 amined through thin glass ; the provision for renewing the supply of 



Fig. 152. 



water without disturbing any part of the apparatus, thus enabling 

 objects to be kept under examination for an indefinite period ; the 

 same arrangement also allowing of the introduction of colouring 

 matters, as carmine, indigo, &c. ; and, lastly, its moderate cost and 

 durability. 



For Confervas, small Infusoria, &c., it is sufficient to place the 

 object on the bottom glass, with a drop of water, and apply the cover- 

 glass in same manner as when using a glass stage-plate, "When a 

 thicker layer of water is required, the ring of vulcanite, cork, or other 

 suitable material, of the requisite thickness, should be placed on the 

 lower glass, and the object put in position, and the cover-glass applied 

 as in mounting objects in liquid in a cell. The supply of water can 

 be maintained by placing a drop occasionally in one of the side 

 " wells," keeping the slide, when not under examination, in a small 

 damp chamber, to prevent evaporation. To change the water, supply 

 through one " well " and draw out through the other by means of 

 blotting-paper. 



Botterill's Life-trough. — Mr. Botterill objects* to the mode in 

 which these troughs f are now made with tliick glass. By using tliin 

 glass for both back and front a half-inch objective will focus up to the 

 back of the trough, and higher powers, say up to the sixteenth 

 immersion, can be used to examine objects on or near the front glass. 

 Thin glass also allows a much better dark ground to be obtained with 

 paraboloid or achromatic condenser. 



With regard to the use of vulcanite, of which the troughs have 

 been largely made,;}: Mr. Botterill prefers brass for general use and 

 where marine organisms are not under examination, as brass allows 

 thinner plates to be used and a flatter bevel consequently to be 



* Sci.-Gossip, 1881, p. IGO. 



t For a description and figure, see this Journal, iii. (1880) p. 148. 



J See this Journal, iii. (1880) p. 1082. 



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