294 PEACTICAL PHOTO-MICKOGKAPHY 



PLATE V, FIG. 4. Cover-glass Preparation of Pigeon's 

 Blood, x 360. 



Double-stained eosin and methylene-blue. 



Objective, 16-mm. apochromat, by Carl Zeiss. 



Projection-ocular, 2. 



Illuminant, round-wick paraffin lamp. Abbe chromatic 

 sub-stage illuminator. The illuminant was placed about ten 

 inches from the sub-stage condenser, and no intervening 

 condensing-lens employed, the image of the radiant itself being 

 sufficiently large to cover the field. The illuminating-cone was 

 reduced so that about two- thirds of the N.A. of the lens was 

 employed. 



Green screen composed of acetate of copper and chromic 

 acid, the acetate of copper being in excess. The source of 

 light was one of low intensity, so that the solutions employed 

 were diluted to half- saturation strength. The thickness of 

 the cell containing the fluid was 2 mm. only, to reduce 

 general absorption of light. 



Exposure, 2 minutes. 



Plate, Barnet rapid orthochromatic. 



Development by pyro-soda, the proportion of pyro 

 being kept somewhat below the normal to ensure detail 

 in the body of the cell being brought out. Such objects 

 generally present no special difficulty, provided they are 

 prepared as cover-glass preparations, and the staining is 

 not too deep. 



PLATE V, FIG. 5. Diatom : Navicula lyra. x 600. 



Objective, J-inch, by J. Swift & Son ; mediar ocular, 3. 



Illuminant, arc lamp of the type already described, with 

 pin-hole indicators and vertical carbons. Current, 10 amperes. 

 Achromatic oil-immersion condenser used dry. Slightly con- 

 vergent beam from a plano-convex lens projected into the 

 back lens of the condenser. A critical image of large iris- 

 diaphragm, the latter placed between the plano-convex lens 

 and sub-stage condenser, projected into the object-plane. A 

 two-thirds cone of light employed. 



Screen, Zettnow's green filter ; thickness, 10 mm. 



Exposure, 2 seconds. 



Wellington orthochromatic process plate. 



Development by pyro-soda, with an increase in the 



