234 THE USE OF THE MICROSCOPE 



Mount ill immersion oil. Use dark field from Nelson's 

 Cassegrain, or Zeiss's Leuchtbild condenser, oil immersed, 

 with ribbon-tungsten filament focused on the object. Use 

 fluorite or apochromatic objective of 1.3 aperture. The 

 organisms show the complementary color to the stain. 



50. Same Object. — Stain well with fuchsin, after fixing 

 as in 47. Wash and dry the preparation. Use a corrected 

 and adjusted aplanatic achromatic condenser (with central- 

 spot diaphragm cutting out about 0.7 aperture), water 

 immersed. Employ apochromatic objective 20, and monoc- 

 ular microscope, with tube length increased by about 35 

 millimeters to compensate for the absence of a cover-glass. 

 Or the binocular may be used, if a dry cover-glass 0.17 

 millimeter thick is put on. (Coles.) 



51. Same Object.— Get some liquid India ink which 

 contains no bacteria or spirochsetes. Test this by making 

 a smear. Mix some of the material with a drop of this 

 India ink, and make a smear as described in 47, on a well- 

 cleaned slide. When dry, mount in immersion oil, under 

 a cover-glass 0.17 millimeter thick. Examine with the 

 highest objectives. 



52. Same Object. — As in 51, but use strong filtered 

 solution of nigrosin instead of India ink. The slide should 

 be cleaned first by rubbing it with dry soap, and polishing 

 this off with dry filter or towelling paper. (Coles.) 



53. Streptococcus in Chains from a Culture. — Prepara- 

 tion as in 47, but stain feebly with fuchsin. Mount in 

 immersion oil, under cover 0.17 millimeter thick, and view 

 with Cassegrain or Leuchtbild condenser, and fluorite or 

 apochromatic objective of 1.3 aperture. 



54. Staphylococcus from a Culture. — As in 53. 



55. Surirella gemma. — In low refractive medium. Obtain 

 washed material of this diatom. Spread on cover 0.17 

 millimeter thick, and mount in agar jelly (with an anti- 

 septic). Seal with paraffin. Examine markings (lines of 

 dots) with water-immersion and oil-immersion objectives. 



56. Same Object. — Mount in air, under cover 0.16-0.17 

 millimeter thick. Examples are spread on a cover-glass, 



