A HUNDRED MICROSCOPICAL OBJECTS 235 



which has been previously covered with a thin layer of 

 hyrax dissolved in xylol, and dried. The cover is then 

 heated sufficiently to melt the hyrax. Good examples 

 show the dots black. 



57. Same Object. — Spread material on a cover-glass 

 0.16 milHmeter thick, in water, and dry by heat. Put a 

 drop of hyrax on a shde, and concentrate by heat. When 

 thick, invert the slide over the cover, and apply pressure. 

 The dots show well, with optimum adjustment, and about 

 1.0 condenser aperture. This may be used as a test object 

 for the highest powers. 



58. Dots of Amphipleura. — Mount material containing 

 Amphipleura pellucida as in 57. The visibility of the trans- 

 verse lines may be used as a test for the adjustments of the 

 condenser and objectives, with a ^^^ to ^{q cone. Use blue- 

 green light, with apochromatic objectives. Put tourmalin 

 before source, and rotate to proper position for best vision. 



59. Nuclei of Yeasts. — Spread actively growing yeast 

 over a slide, as in a bacterial smear. Let it nearly dry in 

 the air, and then invert the slide in chrom-acetic-formalin. 

 Stain with iron-brazihn, and mount in immersion oil. 

 Observe nuclear division. 



60. Circulation of Cytoplasm. — Staminal hairs of Trades- 

 cantia, Zebrina, or Rhoeo, mounted in water. Cover-glass 

 0.17 millimeter thick. Viewed with the 70 apochromatic 

 water-immersion objective. Also to be viewed through 

 apochromatic objective 60, of 1.05 aperture, with the 

 cardioid condenser, and a tungsten-ribbon filament focused 

 on the object in green light. 



ANIMAL OBJECTS 



61. Grasshopper Chromosomes. — Obtain males of Chort- 

 ophaga, Phrynotettix, etc., at the right stage. Kill 

 by crushing thorax. Slit open abdomen, using no water, 

 and smear tubules of testis with a scalpel over large cover- 

 glass 0. 17 millimeter thick. Put the cover quickly on a drop 

 of iron-acetocarmine. Seal with melted paraffin. After a 



