FLUORESCENCE MICROSCOPY 



103 



cal to employ magnifications exceeding 500 times. Metcalf and 

 Patton ( 1944 > also report that with black-white film having a 

 Weston rating of 50, exposures of from 2 sec. to 5 min., with an 

 average time of about 10 sec, are required with a 35 mm. camera. 

 In all fluorescence photomicrography the dark-field stop on the 



Fig. 4. A, Human liver showing collagenous fibers in the periportal field 

 and vitamin A fluorescence in the liver cells. B, Second exposure of the same 

 field; the vitamin A fluorescence has faded. C, Rat liver photographed with 

 sensitized film (Fluorapid) ; a large amount of vitamin A fluorescence in the 

 Kupffer and the liver cells is evident. D, Picture of a liver taken with normal 

 ultraspeed film. From Popper and Elsasser (1941) 



condenser and the filter placed on, or in, the eyepiece or microscope 

 tube to screen out ultraviolet rays must be used. Otherwise fogging 

 may occur from the stray radiation. Metcalf and Patton ( 1944) 

 especially recommend the sodium nitrite filter for color photog- 

 raphy. In order to switch from ultraviolet to visible illumination 

 a piece of opal or ground glass is substituted for the filter placed in 

 front of the light source. 



