ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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(2) The hardening of it so that it may resist, without changing 
form, the action of reagents with which it may subsequently bo treated. 
The fixing agents in use are chiefly osmic acid, chromic acid, per- 
chloride of mercury, or picric acid. 
After hardening, the tissue must be washed, so as to remove all 
traces of the fixing reagent. The washing may be done with water if 
any of the first three agents have been used, but if picric acid has been 
used, then alcohol must be used for washing. 
After this, the water of the tissues must be removed, i. e. the tissue 
must be dehydrated, so that post-mortem decomposition may be pre- 
vented. Dehydration is performed as follows : — Put the object into 
50 per cent, alcohol for 2 hours ; then into 70 per cent, for 24 hours ; 
then into 80 per cent, for 12 hours ; then into 95 per cent, for 2 hours ; 
then into absolute alcohol for a short time. 
The object, dehydrated, must now be cleared, i. e. the alcohol must 
be removed and its place taken by some anhydrous substance, miscible 
with the material used for imbedding. Put some of the clearing medium, 
e. g. cedar wood oil or turpentine, into a test-tube, on to the top of it 
pour a little absolute alcohol ; then the object is put into the alcohol, 
and sinks slowly into the clearing medium. When it has sunk to the 
bottom the alcohol may be drawn off with a pipette. The object may 
now be imbedded. It is removed from the clearing medium and soaked 
until thoroughly penetrated by the imbedding medium. The im- 
bedding medium is hard paraffin. The paraffin is kept at its melting 
point, 45° C., and the object is kept in this for 24 to 48 hours ; then 
the paraffin containing the object is allowed to cool. Cut out the block 
of paraffin containing the object and fix it on a cone of paraffin mounted 
on the object-carrier of the microtome. Pare it square and close 
down to the object on all sides. Set the knife of the rocking micro- 
tome square. Set the block square to the knife-edge. Cut the sections.” 
Imbedding Fresh Tissues in Metal.* — According to Dr. Liebreich 
useful sections may be made from fresh tissues, organs, &c., with a 
razor, if the specimens be firmly imbedded in some soft metal, such as 
tinfoil, old colour-tubes, &c. Owing to its softness the metal is easily 
cut, and not only does not harm the knife, but acts as a support to it. 
The results are said to be very good. 
New Arrangement for Raising the Object in Jung Microtome. j’ — 
Drs. A. and H. Borgert describe the latest arrangement for raising the 
object in the Jung microtome. The object-holder consists of two 
cylinders (fig. 114), the interior one of which supports the object O, 
and fits exactly in the outer one A. The latter carries on the side 
turned towards the knife a rack T, in which an endless screw engages. 
By means of a key fitting over the pin Z, as in a watch, the screw 
is turned and both cylinders are raised together until the exact adjust- 
ment in height of the object is effected. The outer cylinder pos- 
sesses a spring-piece F, and by the pressure against this of the screw 
which passes through the axis of rotation D of the metal block the 
two cylinders are simultaneously fixed in their position. 
* Therapeut. Monatskefte, August 1892. See Centralbl. f. Bakteriol. u. Parasi- 
tenk., xiv. (1893) p. 193. f Zeitschr. f. wiss. Mikr., x. (1893) pp. 1-4. 
