OPERATING-ROOM AND FIXTURES. 63 
a light-proof connection between the screen and 
the microscope during the time of exposure. 
The arrangement of the writer’s operating-room 
is as follows : — 
There are two windows. The one in which the 
microscope is placed is entirely closed by means of 
tongued and grooved boards nailed to the sash 
inside. A metal tube an inch and a half in diam- 
eter is introduced into a circular opening in this 
partition, and this may be moved in and out for 
the purpose of making a connection with the sub- 
stage of the microscope when this is adjusted for 
work. The effect of this arrangement is to ex- 
clude all light from the room except that which 
is admitted to the object through a diaphragm of 
proper aperture, or through the achromatic con- 
denser, if one is used. The glass in the other 
window is covered with two thicknesses of heavy 
yellow envelope-paper. This admits enough non- 
actinic light to enable the operator to work in the 
room. 
The camera recommended in Section III., which 
has a bellows capable of being extended to two 
feet, is suspended from a two by four scantling, 
one end of which is supported on the window- 
casing above the microscope, and the other end 
against the opposite wall (at a lower level, to 
secure the necessary inclination). 
When working with the screen at a distance of 
two feet from the eye-piece of the microscope, this 
camera is sufficient to exclude extraneous light 
from the plate. At greater distances, the connec- 
