SOME PROGRESSIVE EXAMPLES 299 



PLATE VII, FIG. 4. Bacillus typhosus. Cover-glass Pre- 

 paration showing Flagella. x 1250. 



Staining by Van Ermengem's method. 



Objective, 2-mm. apochromat, N.A. 1-40, by Carl Zeiss 

 (corrected for 250-mm. tube-length). 



Ocular -projection, No. 2. 



Illuminant, electric arc, taking 10 amperes. 



Condenser, Swift achromatic. 



Auxiliary condenser, Zeiss No. I. 



Screen, Gifford F-line. 



Plate, Barnet orthochromatic. 



Exposure, 7 seconds. 



Development, pyro-soda. 



PLATE VII, FIG. 5. Micrococcus gonorrhoea. Cover-glass 

 Preparation of Pus. x 1500. 



Stain, Loffler's methylene-blue and eosin. 



Objective, 3-mm. apochromat, N.A. 1-40, by Carl Zeiss. 



Projection-ocular, No. 2. 



Illuminant, lime-light, mixed jet. 



Condenser, Leitz oil-immersion, used dry. 



Auxiliary condenser, Zeiss No. I. 



Screen, filter-yellow-K and eosin. 



Plate, Imperial orthochromatic. 



Exposure, 45 seconds. 



Development, pyro-soda. 



The main difficulty in dealing with such objects, where 

 micro-organisms are lying in or on blood-cells, is to get sufficient 

 depth of focus. The objective used should be of the largest 

 focus that will show the desired structure, as great resolving 

 power is not necessary. Magnification may therefore be 

 obtained by increased ocular-power, or greater camera-length. 

 The sub stage iris- diaphragm may be contracted to about 

 half its full working aperture. 



PLATE VII, FIG. 6. Bacillus of Leprosy in Skin, x 1250. 



Stain, fuchsin and methylene-blue. 



The same conditions apply as in Fig. 5, and the same diffi- 

 culty of obtaining a number of bacilli in the tissue in depth 

 in proper focus will be met with. Such sections are usually 

 not very thin, so that the trouble is further accentuated and 

 can only be met in the manner suggested. 



