112 PHOTOGRAPHING BACTERIA. 
up and out of the way and allow the operator to manipulate the microscope 
before attaching the camera. The bellows has an extension of two feet, 
measured from the eyepiece of the microscope to the focussing screen. This, 
with a two-millimeter objective and projection ocular 4, gives an amplifica- 
tion of one thousand diameters. With less extension of bellows and lower 
objectives amplifications ranging down to ten diameters may be obtained. 
In focussing, the operator can, by standing, observe theimage on the screen 
with a focussing glass and manipulate the fine adjustment of the microscope 
with his hand without using a focussing rod, though a suitable focussing rod 
can be easily fastened to the camera upright if desired. 
Setting Up the Apparatus.—The camera being hung on the rack-work, 
the microscope is placed beneath it, a stage micrometer is placed on the stage 
and a medium-power objective and eyepiece attached to the microscope. 
Light is reflected from the lantern upon the object by the mirror of the 
microscope, the observer accurately centres the micrometer, then removing 
the working eyepiece a projection ocular is inserted, the camera racked 
down, and with the image of the micrometer projected on the camera screen 
the microscope is moved in such position that the centre of the micrometer 
image is exactly in the centre of the screen. This position of the microscope 
is marked once for all, and whenever afterward the microscope is placed in 
the same place the centre of the object will be projected on the centre of the 
screen. To correctly place the lantern, a lower-power objective is used, to- 
gether with a high-power (Abbe) condenser. The cbjective is accurately 
focussed on the lines of the stage micrometer; by adjusting the substage con- 
denser a clear image of the lamp flame is projected on the plane of the ob- 
ject (micrometer) and the lantern is moved to such position that the image 
will be central. If the camera is attached, the image will appear central 
on the focussing screen. ' 
This position of the lantern, like that of the microscope, should be fixed. 
To Photograph.—In photographing by oil light with all but the lowest 
powers some form of substage condenser isnecessary. This is due to the fact 
that the source of light must always be focussed on the object in order to give : 
proper definition. In working with the objectives of four millimetres or 
lower, it will be found advantageous to use objectives of lower power as 
substage condensers, for it will be found that if placed in the substage for 
ordinary work they greatly improve the definition of objects. In fact if may 
be laid down as a general rule that whatever with a given light gives the 
best definition to the observer's eye will give the sharpest photographic image. 
Consequently, in high-power work where a condenser is used it will seldom 
be necessary to change the microscope attachments when a photograph has 
to be taken; for in bacteriological work the Abbe condenser which gives 
good definition will, when properly adjusted, give good photographic defi- 
nition also, statements to the contrary notwithstanding. 
To photograph, place the microscope and lantern in position, light the 
centre wick of the lamp, place a ground glass between the lamp and camera, 
and focus the objective accurately on the object. The ground glass is used 
only to reduce the light which might otherwise injure the observer's eye. 
The ground glass is then removed, a fine wire screen placed close against 
the front of the lantern condenser, and by means of the substage condenser 
an image of the screen is projected accurately on the object. This is very 
important, for it is necessary that the light should be accurately focussed on 
the object in order to produce sharp definition. After focussing the light, the 
screen is removed and an opal glass is putin its place. On looking through 
the eyepiece a clear sharp image of the object. will be seen. If an Abbe con- 
denser is used the iris diaphragm of the condenser should now be carefully 
opened and closed until such an aperture is obtained that to the observer's 
eye the object appears to the best advantage. The opal glass is now removed, 
the camera attached to the microscope, and the projected image focussed on 
the camera screen, preparatory to exposure. 
