SOME PKOGEESSIVE EXAMPLES 297 



Screen, signal-green glass. 



Plate, Wellington orthochromatic process. 



Exposure, 1J minutes. 



Development, pyro-soda. 



PLATE VI, FIG. 4. Koch's Spirillum of Cholera. X 1500. 



(Cover-glass preparation of a pure culture.) 

 Stain, fuchsin. 



Objective, 3-mm. apochromat, by Carl Zeiss. 

 Ocular-projection, No. 2. 

 Illuminant, arc lamp, taking 4 amperes. 

 Condenser, Leitz oil-immersion N.A. 1*40. 

 Auxiliary condenser, Nelson achromatic bull's-eye. 

 Screen, iodine-green saturated solution. 

 Plate, Wellington orthochromatic process. 

 Exposure, 45 seconds. 

 Development, pyro-soda. 



PLATE VI, FIG. 5. Human Hair, showing the Organism 

 of Ringworm (Microsporon audouini) on its surface. X 450. 



Unstained. The hair had been macerated in caustic 

 potash to get rid of some portion of the hair structure and to 

 increase transparency. 



Objective, J-inch, by J. Swift & Son. 



Ocular, none. 



Illuminant, electric arc, taking 4 amperes. 



Condenser, Zeiss -Abbe illuminator. 



Auxiliary condenser, Nos. 1 and II. 



Screen, methylene-blue, aqueous solution. 



Plate, Wellington orthochromatic process. 



Exposure, 40 seconds. 



Development, by metol-hydrokinone. 



The whole difficulty with such a preparation is to obtain 

 sufficient contrast, as the organism itself is very transparent. 

 This can only be effected by reducing the aperture of the sub- 

 stage condenser, so that a narrow illuminating-cone is used. 

 The condenser aperture must be reduced carefully to ensure 

 that no diffraction rings appear round the organism or at the 

 edge of the hair itself. 



PLATE VII, FIG. 1. Bacillus anfhracis. Cover-glass Pre- 

 paration of Blood of Inoculated Guinea-pig, x 750. 



