PLATE 19. 



Illustrating the use of Colour Screens in the Photo- 

 micrography of Coloured Sections. 



The sections were the same as those shown on Plate 18 in their 

 actual colours. 



HOOF OF HORSE (longitudinal section) x 7 



Seibert's No. objective, 36mm. No eye-piece. Watson's 

 Achromatic condenser, back combination. Incandescent 

 gas. No auxiliary condenser. Barnet ortho. plate. 



A Red screen, Wratten's A. Exposure, lOmin. 



B No screen. Exposure, ^ min. 



SECTION OF HUMAN SCALP (horizontal section) x 45 



Seibert's No. objective, 36mm. Watson's holoscopic eye-piece 

 x 10. Watson's Universal Achromatic condenser. Liliput 

 arc lamp. Bull's-eye condenser, parallel light. Wratten's 

 Panchromatic "M" plate. 



G Wratten's B+E screens, giving yellow-green monochromatic 

 light of wave length 5600-6000 A.U. Exposure, 15 sees. 



D Wratten's A+D screens, giving red monochromatic light 

 extending from 6400 to red end of spectrum. Exposure, 

 15 sees. 



A and B were taken on orthochromatic plates. 

 C and D on panchromatic plates. 



A The effect of the red screen is noticeable, making the green and 

 blue-purple parts of the section, to which it is complementary, dark, 

 while the red parts become light, although the plate is not red 

 sensitive. 



B The red parts of the section are darkest on account of the 

 sensitiveness of the plate being least to the light they transmit. The 

 green parts are over-exposed. 



C The green screen emphasizes the difference in colour between 

 the orange and red parts of the hair follicles, the contrast being 

 greatly increased on account of the more complete absorption of the 

 light transmitted by the red parts. 



D The light given by the red screen more nearly approaches the 

 transmission of the follicles, and the contrast between red and orange 

 is reduced. The structure of the connective tissue is better shown 

 by the red light. 



Photos. H. L. H. [To follow Plate 18 and page 160. 



