1896.] MICROSCOPICAL JOURNAL. 197 



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, photography with such plates and yellow- rayed 

 light necessitates long exposure and generally gives im- 



Fig. 3. — Gonococci in urethral pus. x 1,200 diameters. Exix)sed two min- 

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

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

 achromatic condenser in substage. The preparation was double stained 

 with methyl-blue and eosin. The gonococci and cell nuclei being of a 

 color complementary to that of the light fi^lter are indistinct; the cell 

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



By courtesy of Medical Record. 



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 colorr 

 ing of many stained objects, often fails in development to 

 give sufficieut contrast for printing purposes. Theortho- 



