82 THE A B C OF PHOTO - MICROGRAPHY 



Photo-micrographing Bacteria. Bacteriology is 

 so distinctive and important a field of micro- 

 scopical research that I have thought it well to 

 give examples and some brief directions in the 

 photographic aspect of it in a paragraph de- 

 voted exclusively to the subject. It is usually 

 deemed a rather difficult one, but with proper 

 staining of the specimen and a good oil im- 

 mersion lens, it becomes one of the easiest 

 operations in high power photo-micrography. 

 The best stainings for this purpose, in my 

 experience, are carbol fuchsine, haem-alum, 

 gentian violet and Weigert's and Gram's 

 methods. Methyl blue is fairly good but 

 should be used sparingly. Amplifications of 

 1,000 diameters are almost universally adopted 

 in the scientific world as being sufficiently high 

 to show very clearly even the minutest forms, 

 and at the same time quite within the easy 

 reach of a student's microscope and iV oil 

 immersion objective. A substage condenser is 

 indispensable. The Abbe chromatic form will 

 answer but an achromatic is vastly superior, 

 as by its means "critical" illumination and 

 resolution are made practicable. No changes 

 in the optical arrangements from those already 

 described as being necessary with high powers 

 need be made, and it only remains for me to 



