42 ELEMENTARY PHOTO-MICROGRAPHY. 



Jm. OBJECTIVE. 



Transmitted 

 Light. 



Human Blood. "A" eyepiece. Chromatic plate. 

 Green colour screen. Thirty-five minutes. 



' OIL IMMERSION. 



Bacteria. Stained red. "A" eyepiece. No colour 

 screen. Chromatic backed plate. Twelve 

 minutes 



Ditto, with green colour screen. Forty minutes. 



When using the simple enlarging camera, fig. 5, 

 with Ilford special lantern plates and incandescent 

 light, an exposure of fifteen minutes was required 

 for whole insects flattened and mounted on glass 

 slips 3in. by lin. (Extension of quarter-plate 

 camera nine inches, and enlarging camera eighteen 

 inches.) With objects stained yellow the exposure 

 was very much increased. Many such objects are 

 too large for low power microscope objectives. 



