THE MICROTOMIST'S VADE-MECUM

471. Hydrochloric Acid may be taken of 50 per cent.
strength, and then has a very rapid action (Ranvier).             &
472. Picric Acid should be taken saturated.                     gotil
Picro-sulphuric acid should of course be avoided on account     Ojpol
of the formation of gypsum.                                        i
473. Chromic and     Nitric Acid.-Dissolve 15      gr. pure     0ent).
chromic acid in 7 oz. of distilled water, to which 30 minims of   boto
nitric acid are afterwards to be added. Macerate for three or     (%at
four weeks, changing the fluid frequently (Marsh).                 jpette,
474. Glycerin. Alum-Carmine.-It should be remembered           ga60
that these commonly-used reagents dissolve carbonate of lime;     W5n
they must therefore be avoided in the preparation of struc-       b16lae
tures containing calcareous elements that it is wished to pre-    tissUeS
serve (calcareous sponges, echinodermata, &c.).                    Inst(
W4sk1
DESILICIFICATION.                            6oi
475. Hydrofluoric Acid (Mayer's method').-The objects           1n
from which it is desired to remove siliceous parts are brought     g
in alcohol into a glass vessel coated internally with paraffin    genent
(otherwise the glass would be corroded by the acid). Hydro- ckrat
fluoric acid is then added drop by drop (the operator taking       ean
great care to avoid the fumes, which attack mucous mem-           t So
branes with great energy). A Wagnerella borealis may thus         (Se
be completely desilicified in a few minutes. Small pieces of      (18v0
siliceous sponges will require a few hours or at most a day.       4
The tissues do not suffer; and if they have been previously       acid,
stained with acetic acid carmine, the stain does not suffer; at   Boakf
least this was so in the case of Wagnerella.                       Th
(As regards sponges, I would point out that if well im-
bedded, good sections may be made from them without pre-
vious removal of the spicula. The spicula appear to be cut;
probably they break very sharply when touched by the knife.
Knives are of course not improved by cutting such sections.)
I ' Zool. Anz.' (1881), No. 97, p. 593.

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