SOME PKOGEESSIVE EXAMPLES 298 



Zeiss projection-ocular, 2. 



Camera -length, 2 ft. 10 in. 



Illuminant, mercury-vapour lamp. 



Sub-stage condenser, Swift apochromatic, N.A., 0-95. 



Auxiliary condenser-plano-convex lens, with plain surface 

 towards the illuminant, the image of the illuminant being 

 focussed at the plane of the sub-stage iris-diaphragm. Auxili- 

 ary iris-diaphragm interposed between the illuminant and 

 auxiliary lens. Critical image of the opening in the latter iris- 

 diaphragm projected into the objective plane. Sub-stage 

 iris closed, so that about two-fifths of the total aperture of the 

 objective was used. 



Plate, Wellington process orthochromatic. Tartrazine and 

 filter-yellow-K fluid screen. The whole of the blue-violet 

 and ultra-violet light emitted by the mercury- vapour lamp 

 eliminated. 



Exposure, IJ minutes. 



Development by pyro-soda. A developer containing 

 rather more than the usual quantity of pyro, and a few drops 

 of a 10 % solution of potassic bromide were used to secure 

 contrast. 



As with all diatoms, the important point is to see that the 

 sub-stage iris-diaphragm is not closed sufficiently to produce 

 diffraction images around the outer edge of the frustule, or 

 around the secondary markings. 



PLATE V, FIG. 3. Tripanosoma gambiense. X 1000. 



Stained by Komanowsky-Leishman method. (Methylene- 

 blue-eosin.) 



One-twelfth-inch objective, by C. Baker. 



No ocular. 



Short thick velvet sleeve inserted in top of microscope body- 

 tube to stop reflection. 



Abbe chromatic condenser. 



Plano-convex auxiliary lens giving a parallel beam. 



Illuminant, mercury-vapour lamp. 



Green screen as in Plate V, Fig. 1. 



Plate, Barnet orthochromatic. 



Exposure, 5 minutes. 



Development with pyro-soda. 



