22 Transactions of the Society. 



In conclusion, unless a good picture is portrayed upon the 

 ground-glass screen to the naked eye without the use of a magnifier, 

 just as in ordinary photography, the resulting negative will probably 

 be a failure, but by the use of the above simple filters, supplemented 

 by the spectroscope, much may be accomplished upon subjects 

 hitherto considered impossible, and in all cases much useful infor- 

 mation may be acquired. 



EXPLANATION OF PLATE I. 



Fig. 3. — Trypanosoma gambiense. x 1500. Leitz objective ; ^oil-immersion; 

 6 x compensating ocular ; Barnet ortho plate ; Nernst lamp. Ex- 

 posure, 3 minutes. 



,, 4. — Bacillus pestis. x 1200. Potassium bichromate filter. Exposure, 

 3 minutes. 



,, 5. — Poison fang of Spider. Gentian-violet filter. Exposure, 10 seconds. 



,, 6. — Gizzard of Cricket, showing teeth. Gentian-violet filter. Exposure, 

 10 seconds. 



