PHOTOGRAPHING BACTERIA. 113 
Plate Used.—Orthochromatic plates only should be used. Of these I use 
the Cramer rapid, isochromatic plate exclusively. With these when photo- 
graphing bacteria and using an amplification of one thousand diameters the 
exposure will vary from one and one-half to three minutes, two minutes 
being about the average. 
It is with these plates that I have found a color screen unnecessary, and 
since using them I have had no difficulty in photographing bacteria, for they 
are particularly sensitive to the yellow-colored oil light. 
Possibly other makes of orthochromatic plates might be found to work 
equally well, but the oil light works so very well with the Cramer isochro- 
matic that I have had no desire to try others. 
Development.—¥Yor development, I have obtained best results with for- 
mulas in which hydrochinon either alone or with some other developing 
agent is used. The following gives excellent results, and I prefer it to other 
developers as it gives good clear negatives of sufficient contrast and 
gradation: 
No. 1. 
Water, .| 3 ‘ i : : : 10 ounces. 
Sodium sulphite,  . ; : 1 ounce. 
Potassium bromide, : ‘ ‘ : 10 grains. 
Hydrochinon, . : . 30 grains. 
Metol, 3 ‘ i ‘ ‘ 3 : 40 grains. 
No. 2. 
Water, , i ‘ ‘ : : . 10 ounces. 
Sodium carbonate, 
: ‘ 300 grains. 
Use equal parts of No. 1 and No. 2. 
Development should be continued until sufficient density is obtained. In- 
tensification should be rarely required, for with proper exposure and develop- 
ment a good negative can usually be obtained. If intensification is neces- 
sary, after fixing and washing the plate, I prefer to use a saturated aqueous 
solution of bichloride of mercury, followed by washing, the application of 
dilute ammonia water, and a final washing. 
Students who desire to perfect themselves in the art of making 
photomicrographs are advised to first make themselves familiar with 
the technique of photography with a landscape or portrait camera, 
and not to undertake the more difficult task of photographing bac- 
teria until they know how to make a good negative and to judge 
whether an exposure has been too long or too short, ete. 
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