106 PRACTICAL PHOTOMICROGRAPHY. 



dense yellow object on a pure white ground,or a very pale yel- 

 low or pink of such a nature that the contrast between object 

 and ground is very small. Color- correct photography helps us 

 out of all these troubles and many besides ; and it may be 

 stated once more, as it has been stated by the writer on former 

 occasions, that no branch of photography has been so much 

 benefitted by " ortho-chromatics " as photo-micrography, and 

 that in color-correct photography lies the future of photo- 

 micrography. The writer has lately produced such renderings 

 of double stained pathological subjects, prepared without 

 regard to photographic requirements, as a few years ago neither 

 he nor any other person would have been mad enough to 

 attempt. 



The advances that up to this date have been made in ortho- 

 chromatics may be summed up briefly in the statement that 

 our plates have been rendered more sensitive to yellow-greens, 

 yellows, oranges and reds than they could be made formerly, 

 and less proportionately sensitive to blue-greens, indigos, blues 

 and violets. Plates have even been prepared as sensitive to 

 yellow as to blue ; but our usual procedure is to make a plate 

 more sensitive to yellows, etc., than an ordinary plate, and a 

 little less sensitive to violets and blues, and to assist the action 

 when necessary by calling off more or less of the blue and 

 violet by means of yellow " screens." By this method we 

 have more command over our results than if our plates were 

 as sensitive to yellow as to blue ; indeed, if we carried the 

 sensitiveness too far into the red end of the spectrum, we 

 should often have to cut off some of our yellow rays, and we 

 should have great difficulty in finding a suitable light whereby 

 to develop our plates. Still, for a few subjects, a greater 

 sensitiveness to red would be a great boon, though developing 

 difficulties would multiply. 



In Britain, at least, color-correct gelatine bromide plates 

 may be bought ; as a rule, they keep quite well for a few 

 weeks, but we prefer to use them within a few days. Mr. B. 

 J. Edwards, working under the " Tailf er-Clayton " patent, 

 produces plates orthochromatized by an eosin process; Mr. 

 J. R. Gotz trades in plates sent from Germany by Vogel and 



