170 THE USE OF THE MICROSCOPE 



ill iroii-acetocarmine or immersion oil, the groups being 

 flattened out in the cytoplasm on the cover-glass, or on the 

 slide. 



Mazda-C lamp, 110 volts, 103 watts, end on, with 

 condensing lens and ground-glass disc in front, this disc 

 being ground on both sides and treated with magnesium 

 sulphate. Diaphragm equalling field of view and close to 

 ground glass. Wratten yellow-green screen, No. 56. 

 Reflecting prism. Corrected water-immersion condenser 

 giving 1.2 sohd cone. Slides 0.9 to 1.1 millimeters thick. 

 Covers, 0.17 millimeter. Iron-acetocarmine (or immersion- 

 oil) preparations. Water-immersion apochromatic objec- 

 tive 70 of 1.25 aperture, or oil-immersion objective 90 of 

 1.4 aperture. Homal lens IV for high-power immersion 

 objectives. Phoku camera with Goldberg wedge. Agfa 

 non-halation isochromatic plates. Rodinal developer. 

 Enlargements are made on lantern slides and negatives 

 made from these, from which the final positives are taken 

 (see Figs. 22 and 23). 



Practical Points 



1. Use a projection eyepiece or a homal negative lens, both of 

 which are specially calculated for photography; not eyepieces 

 which were calculated for direct vision; or add a small camera 

 lens, above eyepiece. 



2. The side tube, by which the object may be focused and 

 viewed during exposure, is useful for quick work. 



3. The graduated Goldberg wedge enables the exposure to be 

 determined with accuracy. 



4. It should be possible to take a high-power photograph in 

 about 15 minutes, everything being replaced, and the plate 

 developed. 



5. A suitable small diaphragm on the source of light prevents 

 fogging of the plate, and renders wide tubes and velvet lining 

 superfluous. 



6. The focus may sometimes be altered during exposure, for 

 parts of the object at slightly different levels. 



7. Preparations might well be specially stained for 

 photography. 



8. The Siedentopf and other miniature attached cameras allow 

 of easy photography, and thus of skill gained by practice. 



