OPERATING-ROOM AND FIXTURES. 61 
object in view, as this change from a horizontal 
position is made at the sacrifice of some conven- 
ience as regards working. 
It is evident that the scantling supporting the 
movable screen must have exactly the same incli- 
nation as that given to the microscope, so that the 
centre of the screen, in any position, may corre- 
spond with the optical axis of the instrument. 
This being the case, the operator can no longer 
stand erect before the screen when it is removed 
to its most distant point. In practice, it will be 
found most convenient to place the shelf upon 
which the microscope is supported at a greater 
elevation than when the instrument is in a hori- 
zontal position, in such a manner that the operator 
may still stand erect, or nearly so, when focusing 
upon the screen at its most distant point. This 
makes a little platform necessary just in front of 
the microscope, upon which the operator stands 
when working with the instrument. 
The views obtained in a dark room through an 
instrument mounted in this way, either with or 
without an achromatic condenser (without helio- 
stat), are so satisfactory, that it is worth while for 
one who does much work with the microscope to 
devote a room to this purpose, even if he does not 
propose to make photo-micrographs. 
In many of the laboratories devoted to instruc- 
tion in biology, histology, or pathology, the students 
may be seen seated before their microscopes at 
work under conditions as to illumination which fall 
very far short of the ideal illumination obtained 
