9 
rapid exposure with, an excess of light does not give the details 
which are obtained with less light and a longer exposure. In a 
general way then it may be said that the intensity of light should 
be subdued by reducing the diaphragm in the Abbe condenser 
until the exposure will approximately require about five seconds. 
Care should be taken to see that no vibrations are produced 
during the exposure. This is best accomplished by selecting a 
time when the streets are free from passing vehicles, and all in 
the room should remain quiet. An ordinary pneumatic photo- 
graphic shutter in the front board serves to reduce vibrations to a 
minimum and is far superior to the regular shutter supplied with 
these cameras. 
CHOICE OF PLATES 
Only plates of double coating should be selected for this work, 
X^referably one of the medium or slow grades. 
They are distinguished from the ordinary plates by their iso- 
chromatic or orthochromatic qualities, giving correct color values 
Avith double-stained preparations — a property that can be increased 
by using a color screen complementary to the object to be photo- 
graphed. 
As a rule Avith these plates, no color screen is required with 
fuchsin, safranin, luematoxylin, or carmine. 
Without reference to the complementary color, a color screen 
made with chromic acid or sulphate of copper, or both, combined 
in weak solution Avill answer for any color or combination of colors 
in general laboratory use. 
DEVELOPAIENT. 
A good developer has the property of producing both detail and 
density. A single developer does not possess these qualities per- 
fectly, so a combination is used. 
Metol and hydrochinone about rei)resent the extremes, but when 
combined in |)roper proportions give the best results in micro- 
photographic work, as Avell as in general photography. The for- 
mula most used is the following : 
n 
Metol ‘2.00 
Hydrochinone 2.00 
Sodium suljdiite . 20.00 
Sodium carbonate 10.00 
Potassii broniidi 0.25 
Distilled water 500.00 
M. 
