PLATE 14. 



Photomicrography of Insects. 



Illustrating the use of a blue screen to increase contrast, and the 

 disadvantage of noii-colour-serisitive plates. 



A WINDOW GNAT x 7 



Objective Ross Planar, 3". F. 4.5. 



Condenser ... Lantern condenser and ground glass. 

 Illuminant ... 30 c. p. electric metal filament lamp. 



Screen Wrattcn's H, blue. 



Plate Imperial ordinary. 



Exposure 1 min. 



Photographed with the apparatus indicated by Fig. 43. The ordinary 

 plate is not capable of showing the detail in the denser brown parts 

 of the thorax; these are, however, readily reproduced on ortho. or 

 panchromatic plates, which should always be used for objects of this 

 sort. The contrasts arc increased still more by the blue screen, in 

 this case giving an improvement in the wings and abdomen but 

 not elsewhere. 



B LOUSE OF GAT x 70 



Objective Swift's i". N. A. 0.88. 



Eye-piece None. 



Condenser ... Abbe. 

 Illuminant ... Incandescent gas. 

 Aux. Condenser \oiie. 



Colour Screen ... Deep blue. Ammoniacal copper sulphate 

 solution. 



Plate Imperial Special Rapid Ortho. 



Exposure 1 min. 



The colour of this specimen was very pale yellow, and scarcely 

 differentiated from the balsam in which it was mounted. A deep- 

 blue screen was therefore used to give as great contrast as possible, 

 and the iris of the condenser carefully closed down to help in the same 

 direction, but not far enough to produce diffraction effects. 



Photos. H. L. H. 



W. B. R. \Tofollowpage132. 



