A HUNDRED MICROSCOl'ICAL OBJECTS 2:VA 



use a central stop just largo enough for the 20 apochronuiMc 

 objective of 0.05 aperture. For all these, the best radiant 

 is probably the ribbon of a tungsten ribbon-filament, 

 6-volt, 108-watt lamp, focused directly on the object, and 

 moderated by yellow-green or blue-green screens. Observe 

 the bacteria dividing transversely, and the spirochastes 

 dividing longitudinally. 



46. Same Object. — Observe with yellow-green or blue- 

 green light, corrected water-immersion condenser, cover- 

 glass just 0.17 millimeter thick, diaphragm on source 

 smaller than source-field, and water-immersion objective 

 (70 apochromatic, or 90 achromatic). 



47. Same Object. — Smear uniformly on slide with end of 

 other slide held obliquely, with the Uquid in the acute angle, 

 and this angle preceding the obtuse angle. Allow to nearly 

 dry. Fix sUdes in Flemming's solution, or in chrom- 

 acetic-formaUn. Stain with gentian-violet and iodine, or 

 with iron-haematoxylin in 70 per cent alcohol. Mount 

 in immersion oil with standard cover-glass; or examine 

 without a cover, lengthening the microscope tube in the 

 latter case (by about 15 milUmeters for a 90 objective). 

 Use an apochromatic objective of 1.3 or 1.4 aperture with 

 Wratten screen No. 56; or a fluorite objective of 1.3 aperture 

 with Wratten screen No. 58. 



48. Same Object. — Smear on cover-glass 0.17 millimeter 

 thick, and fix and stain as in 47, taking care that the back- 

 ground is clear. The finest rods, cocci, and spirochsetes will 

 then be Hghtly stained. Wash well in xylol, and dry 

 over fused calcium chloride. Mount in air, with melted 

 paraffin round the edges. Observe with apochromatic 

 oil-immersion objectives of 1.3 and 1.4 aperture, with 

 maximum condenser cone of 1.0. Since the objects are 

 in optical contact with the cover-glass, the working aper- 

 tures will be 1.15 and 1.2, respectively. Minute bacteria 

 and flagella are clear. 



49. Same Object. — Stain hghtly with fuchsin, after 

 preparation as in 47. Use sUde of the right thickness to 

 suit the condenser, and cover-glass 0.17 millimeter thick. 



