152 SUMMARY OF CURRENT RESEARCHES RELATING TO 



C5) Mounting-, including Slides, Preservative FluidSj &c. 



Preparation of Type-plates and arranged Groups of Diatoms.* — Mr. 



K. M, Cunningham says that Mr. E. Getschmann prepares his slides of 

 arranged diatoms after the following method : — 



A table is placed before a well-lighted window, and on this are 

 the requisite appliances for work, the chief requisite being a small 

 dissecting Microscope, fitted with simple achromatic lenses, varying 

 in their focal length as the case might require, but a lens of about 

 1/4 in. focus answering for actual work. Preparatory to begin- 

 ning a selection of diatoms for the design to be arranged, a quantity 

 of cleaned diatom material is evenly spread over an ordinary slide, 

 this is carefully examined, and from it are selected all the perfect 

 forms likely to be used in a design, and transferred to a cover-glass ; all 

 forms of the same shape being grouped together, or arranged in lines for 

 convenience afterwards. If necessary, several cover-glasses can be thus 

 filled with perfect forms, free from cracks or other blemishes, and placed 

 aside, protected from dust, until required. The diatoms are picked out 

 from the spread layer of material by the aid of hair bristles of varying 

 degrees of fineness mounted in a slender wooden handle, and projecting 

 therefrom about a half-inch ; the bristle should be straight and, if 

 possible, have a fine taper to a sharp point ; this is used with a free and 

 steady hand, and, to facilitate steadiness in jjicking out, the two arms are 

 rested upon two cushioned blocks of wood, tapering from the level of the 

 stage of the Microscope to their bases on the table. A further indispens- 

 able piece is a glass slide, having an area at its centre of about a quarter 

 of an inch, or somewhat less, ruled into minute squares at the rate of 

 about forty lines to the quarter-inch ; on this slide, and properly centered, 

 must be placed the cover-glass upon which it is desired to produce the 

 group. The cover-glass is prepared by spreading at its centre a minute 

 drop of liquid gelatin, by means of a little brass spatula, and allowing it 

 to dry. A number of cover-glasses, after having been carefully chosen 

 and thoroughly cleaned, might be prepared, and also set aside for use 

 later. The clear and transparent gelatin should be filtered before use by 

 passing it through suitable filter-paper, so as to prevent all chance dirt 

 from marring the mount. Wh^n ready to begin a group, fix the cover- 

 glass centrally over the area of squares by means of three little touches 

 of wax, and then also adjust, close to the same cover-glass, one of the 

 cover-glasses containing the diatoms previously selected for the grouping ; 

 or, if necessary, two or more, according to the complexity of the proposed 

 design. With the selecting bristle in the right hand, and the eye 

 adjusted to the lens, bring the glass containing the selected diatoms into 

 the field of view, then carefully select as a centre a perfect disc, say, a 

 Coscinodiscus ; now shift the gelatined cover-glass into view and deposit 

 the disc at its centre, and carefully adjust it so that its centre shall seem 

 to cover the intersection of a group of the small squares ; around the disc, 

 as a centre, adjust a series of small circular forms, spacing them at 

 equal distances from each other. Should it next be desired to introduce 

 a series of slender forms they may be adjusted into position by lining 

 them over the guide lines radiating from the centre of the disc, or through 

 the diagonals of the squares ; in this manner proceed until the design is 

 completed. 



* The Microscope, viii. (1888) pp. 237-41 (2 figs.). 



