ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 805 



fresli water is constantly percolating the cell, and regulating the 

 temperature will be self-evident. 



The slide consists of a slip of non-oxidizing metal If by 3^ by 1/8 in., 

 having a central opening of 1/2 in. D, with a disc of glass forming 

 the bottom of the central cell, and fitting flush with the underside of the 

 base, allowing of illumination with a paraboloid. Surrounding the glass 

 on the upper surface is a slightly raised edge of metal forming a central 

 flat cell, having a uniform depth about equal to the thickness of ordinary 

 blotting-paper. Outside this central cell is a slight recess in the metallic 

 base, which forms an annular cell C, surrounding the central one through 

 which water percolates when in use. The central and annular cells are 

 closed by means of a thin cover-glass, cemented to a rim of metal E, which 

 fits watertight over the two cells ; the under surface of the cover-glass being 

 held close against the raised edge of metal forming the boundary of the 

 inner cell, thus closing and preventing the escape of organisms placed 

 therein. There is water communication between the central and annular 

 cells, by a series of very fi.ne capillary lines, ruled in the metallic edge 

 between the cells. 



On each end of the metallic base is fixed a reservoir A having a glass 

 cover. These reservoirs are directly connected with the annular cell by 

 fine tubes B, through which water flows when in use from one reservoir 

 to the other. 



The action is as follows : — Organisms are placed in the central cell 

 and the cover-glass pressed tightly down ; one of the reservoirs is then 

 filled wdth water and the circulation established. If the slide be now 

 placed on the stage of a Microscope provided with a revolving slide 

 carrier so that the full reservoir is highest, the water will flow through 

 the fine tube to the annular cell ; a portion of which will percolate to the 

 inner cell by capillary motion, and thence through the second tube into 

 the other reservoir. When the upper reservoir is empty the motion may 

 be reversed, thus enabling a constant circulation to be kept up during 

 microscopic examination. Each reservoir is provided with a small air- 

 vent, drilled coincidently through the upper edge of the reservoir and 

 the rim of the cover. These vents may be entirely closed when 

 desirable, by simply turning the covers slightly round so that the holes 

 do not coincide. The flow of water may also be regulated, by placing 

 bristles within the fine tubes leading from the reservoirs to the annular 

 cell. 



To continue the water circulation when off the Microscope several 

 methods are available, two of which I will here mention. The method 

 which recommends itself as the simplest, and perhaps gives the best 

 results, consists of a stand or support for carrying the slide and large 

 supply reservoir for containing enough water to last several days. The. 

 supply ve-sel is placed at a higher level than the slide, and a siphon 

 may be used to convey water from this vessel into one of the reservoirs. 

 A suitable siphon is easily made by bending a length of vaccine tube (to 

 be had from most chemists) having a short piece of thi'ead pushed inside 

 the long end to regulate the drip. Another shorter siphon made from 

 the same material is placed in the hole near the top of the other reservoir, 

 to conduct the overflow into a vessel placed beneath. A better arrange- 

 ment is obtained when the supply cistern is fitted with a miniature water- 

 tap near the bottom, the water being allowed to fall in drops into the first 

 reservoir of the slide, and flow out as before stated. 



1888. 3 I 



