1896.] 



MICROSCOPICAL JOURNAL. 



I'JV 



This objection does not obtain when these lights are 

 properly used or when used with orthochromatic plates 

 The ordinary commercial dry plates are mainly sensitive 

 only to the more actinic rays of the violet end of the 

 spectrum, and oil and gas light being deficient in these 

 rays, pliotogra})liy with such plates and yellow- rayed 

 light necessitates long exposure and generally gives im- 



Fig. 3. — Gonococoi iu urethral pus. x 1,200 diameters. Exposed two min- 

 utes to acetylene light with yellow-light filter, usiug Zeiss' two milli- 

 metre apochromatic objective, projection eyepiece No. 4, and with Abbe 

 achromatic condenser in substage. The preparation was double stained 

 with methA-l-blue and eosin. The gonococci and cell miclei being of a 

 color complementary to that of the light filter are indistinct; the cell 

 bodies being of a similar color to the screen, are indistinctly photographed. 



By courtesy of Medical Kecord. 



perfect results' As with sunlight, the difference between 

 the visual and actinic focus enters as a disturbing factor, 

 necessitating troublesome and uncertain adjustments or 

 the employment of specially constructed objectives. Also 

 the violet sensitive plate, owing to the like actinic color- 

 ing of many stained objects, often fails in development to 

 give sufficient contrast for printing purposes. The ortho- 



