12 THE AMERICAN MONTHLY [Jan 



tereated in the subject, I would refer to ray papers in the 

 journal of the Royal Microscopical Society of 1896, pp. 

 373-88, and in the Quekett Club Journal, 1897, p. 346, 

 and 438. 



EXPLANATION OF DIAGRAMS. 



Fig. 1. Various Colors Discs. 



Fig. 2. First Method of Multiple Color Illumination 

 — No object in the field. 



Fig. 3. First Method of Multiple Color Illumination 

 — Object in position. 



Fig. 4. Second Method of Multiple Color Illumina- 

 tion — No object in tlie field. 



Fig. 5. Second Method of Multiple Color Illumina- 

 tion — Object in position. 



Fig. 6. Diffraction Fan produced by a ray of Light 

 R passing by or through an obstacle S. 



Fig. 7. Third Method of Multiple Color Illumina- 

 tion — No object in the field. 



Fig. 8. Third Method of Multiple Color Illumination 

 — Object in position. D, Color Disc ; C Condenser ; S, 

 Object; 0, Condenser ; G, Iris Diaphragm. 



Dotted vertical lines represent the passage of white 

 light. Slanting shading represents dark space. 



Preserving as Permanent Specimens Casts Found in Urine. 



Generally speaking, all crystalline substances found in 

 urine can be preserved in Canada balsam after allowing 

 them to dry on a slide or cover glass. However, speci- 

 mens thus mounted are likely to become cloudy in from a 

 few weeks to two years. Shreds of tissue, parasites and 

 their ova, are well preserved when mounted in glycerin, 

 as are unstained bacteria and fungi. 



It is far more difficult to make satisfactory mounts of 

 casta, since their general characteristics are so readily de- 



