SOME PKOGRESSIVE EXAMPLES 289 



Camera-extension, 2 ft. 6 in. 



Exposure, 1J minutes. 



Development by pyro-soda. 



It will be seen that, in spite of the faint staining of the 

 specimen, the use of a suitably adjusted screen of deep colour 

 has enabled the differentiation of structure to be well brought 

 out ; in fact, judging from the photograph, there is no 

 indication that the specimen was not a good one. 



PLATE III, FIG. 3. Group of Foraminifera. x 25. 



Transparent object. 



Objective, 1-inch achromatic, by W. Watson & Sons. 



No ocular. 



Illuminant, electric arc, taking 10 amperes. 



No sub-stage condenser. 



Illumination by slightly convergent beam projected by 

 Nelson's achromatic bull's-eye. 



Screen, filter-yellow K and tartrazine. 



Camera-extension, 1 ft. 9 in. 



Plate, Wellington orthochromatic process. 



Exposure, 2 seconds. 



Development with pyro-soda, somewhat restrained with 

 potassium bromide to ensure maximum contrast. 



Such an object presents no particular difficulty, except 

 that it is advisable to use a lens of as long focus as possible, 

 and with the smallest working N.A. that will bring out .the 

 required detail, thus ensuring maximum penetration. 



PLATE III, FIG. 4. Medulla of Monkey, x 15. 



Staining, Weigert haematoxymi. 



Objective, Zeiss 75-mm. micro-planar, mounted on front 

 of camera. 



No ocular. 



Illuminant, Leitz electric arc, taking 4 amperes. 



Sub-stage condenser, Watson's macro-illuminator. 



Convergent-beam projected into condenser by means of 

 ordinary bull's-eye as supplied with Leitz electric lamp. 



Screen, saturated solution of auramin. 



Plate, Wellington orthochromatic process. 



Exposure, 10 seconds. 



Development, pyro-soda. 



