290 PEACTICAL PHOTO-MICKOGEAPHY 



PLATE IV, FIG. 1. Impression Preparation of Bacillus 

 antliracis. x 100. 



Stain, methylene-blue. 



Objective, J-inch achromatic, by Charles Baker. 



No ocular. 



Illuminant, Nernst electric lamp, taking 1 ampere. 



Condenser, Abbe chromatic, working at full aperture. 



Auxiliary condenser, Zeiss Nos. I and II collecting -lenses. 



Screen, saturated solution of bichromate of potash. 



Camera -extension, 2 ft. 



Plate, Barnet orthochromatic. 



Exposure, 40 seconds. 



Development, pyro-soda. 



PLATE IV, FIG. 2. Colony of Bacillus coli communis, on 

 Gelatin Plate, x 50. 



Objective, 1-inch achromatic, by W. Watson & Sons. 



No ocular. 



Illuminant, electric arc, taking 10 amperes. 



No sub-stage condenser. 



Oblique illumination obtained by projecting a slightly 

 convergent beam on to the mirror of the microscope, the latter 

 being thrown well to one side. 



Screen, Gifford F-line. 



Camera-extension, 3 ft. 



Plate, Wratten & Wainwright's lantern. 



Exposure, 30 seconds. 



Development by metol-hydrokinone. 



In photographing such an object in order to bring out the 

 reticulated surface-structure suitable obliquity of the light 

 is the essential point, and this can only be arrived at by ex- 

 periment. The beam should first be projected at the smallest 

 possible angle to the optical axis, and this angle gradually 

 increased until the desired effect is obtained. The least 

 possible obliquity of the beam should be used that will show 

 up the structure, to avoid the introduction of diffraction effects 

 that would otherwise interfere with the formation of a good 

 image. 



PLATE IV, FIG. 8. Group of Mixed Diatoms, x 100. 

 Objective, -inch, by James Swift & Son. 



