MICROSCOPE. 
be found much superior to any form of knives 
for cutting through delicate tissues without 
disturbing them. Swammerdam is said to 
have made great use of such implements, in 
his dissections of insect structures, which, 
from the accounts of them on record, seem 
almost to have surpassed any which have been 
since executed. The curved forceps recom- 
mended by Mr. Slack, we also have used with 
much advantage. For more minute dissection 
we can strongly recommend common needles, 
and cutting implements which may be easily 
manufactured from them, by grinding down 
their sides upon a hone. These may either be 
fixed in wooden handles, or, which is much 
better, held in little instruments resembling 
crayon-holders, specially constructed for their 
reception. The dissector is thus enabled to give 
to his needle the effect of a long elastic point or 
of a short stiff one, by simply altering the part 
at which it is held. In the ivory handles 
of these holders, also, there is a receptacle for 
the needles, which makes the whole of this 
useful little apparatus complete in itself.* 
Many microscopists, especially on the conti- 
nent, are in the habit of making great use of the 
compressorium, an instrument in which an ob- 
ject may be submitted to graduated pressure 
etween two plates of glass, the parallelism of 
which is perfectly maintained. The results 
obtained by such compression, however, must 
be accepted with great caution, and need to be 
corrected by those views of the object which 
are gained without that distortion of it to which 
itis liable in this method. The class of inves- 
tigations in which the compressorium is most 
valuable, is that in which such structures as the 
minute ovum need to be closely scrutinized, 
without any further change in their shape than 
may render their contents more distinctly visi- 
ble. For such purposes we believe that a 
steady hand and a well-made aquatic box will 
answer the purpose sufficiently; but to those 
who prefer relying on mechanical assistance, 
the compressorium will be a useful instru- 
ment. 
We shall now proceed to describe some of 
the modes of mounting and arranging simple 
and compound microscopes, which appear to 
us most convenient. The first that we shall 
notice is a form which has cheapness and sim- 
plicity to recommend it, and which, if well 
made, is capable of an adjustment sufficiently 
delicate for all ordinary purposes. It is a 
slight modification of one of Mr. Pritchard’s.+ 
A (fig. 166) is the stand, or basis, into which 
the pillar is screwed. This may be variously 
constructed, according to the purpose for which 
it is designed. If bulk be an object, it may be 
around disk of lead; but if weight must be 
avoided, a thick tablet of mahogany about six 
inches square, or five inches by seven, (the 
longest side being in the direction of the 
movement of the pillar,) is preferable. If great 
* Such needle-holders are sold by Mr. Pritchard, 
Fleet-street, London. 
+ Microscopic Illustrations, 2nd ed. p. 82. 
347 
eae” 
SoA 
Rs 
Elevation of ordinary compound or simple microscope, 
A, base; B, hollow pillar, with joint at bot- 
tom; C, triangular rack; D, nut by which it 
is moved; E, bar carrying compound body ; F, 
other end adapted for simple magnifiers; G, 
compound body; H, objective; I, spring fork ; 
M, mirror attached to sliding tube, tightened by 
the nut, N; S, stage. 
portability be desired, the pillar may be made 
to screw into the top of the box that holds the 
apparatus; but this plan should notbe adopted, 
unless all the smaller fittings be contained in a 
tray which may be lifted out, in order that 
there may be no necessity for opening the box 
when the instrument is in use. The pillar isa 
thick tube of brass about six inches long, with 
a large screw at the bottom for being attached 
to the stand, and a joint above this, for allow- 
ing it to be inclined at any angle. If this joint 
be well constructed, the instrument will remain 
in any position in which it is placed, without 
any steadying rod or perceptible vibration. 
Within the tube is a triangular bar, with a rack 
cut on its posterior edge; this may be raised 
or depressed from the top of the tube, by turn- 
ing the milled head, which carries a pinion 
working into the rack. Partieular attention 
