OF MICROSCOPIC OBJECTS. 205 
citric acid solution, with the addition of a little: alcohol. 
The fixing may be effected by a strong solution of hypo- 
sulphite of soda, and the picture should then be very well 
washed with pure water. When dry, the photograph must 
be mounted with Canada balsam, in the same manner as 
any ordinary object; but great heat must not be used, or 
the picture may be injured. 
When ordinary daylight is employed for this purpose, a 
dark slide will be required for the prepared plate, in the 
same way as for photographing landscapes, &c. These 
dark slides are generally made by each individual to suit 
his particular arrangements of negatives; but it may 
be here recommended that the operator shouid always 
focus.in the same slide which he is about to use, as sc 
small a difference in distance lies betwixt perfection and 
failure. 
For an ordinary student, perhaps the preceding method is 
that which is the most readily used, and consequently the 
most generally available; but almost every one has a dif- 
ferent arrangement of microscope, by which he procures 
these minute pictures. Mr. Shadbolt (one of our most 
successful photographers) gives the following instructions :— 
“ Having removed the upper stage-plate of a large com- 
pound microscope, I replace it with one of wood, supplied 
with guide-pins of silver wire, in order to admit of its sup- 
porting a slip of glass coated with collodion, and excited in 
the nitrate of silver bath in the usual way. If the ordi- 
nary brass stage-plate were left undisturbed, it is obvious 
that it and the excited slip of glass would be mutually 
destructive. 
“The microscope is now to be placed in a horizontal 
position, the objective, intended to produce the picture, 
made to occupy the place usually filled by the achromatic 
condenser on the sub-stage of the microscope, while another 
objective is screwed into the lower end of the body of the 
instrument, which is used not only to focus with, but also 
to make the requisite allowance for actinic variation. 
