ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
687 
Heat absolute alcohol to 50° C., saturate with picric acid, and then 
add bichloride of mercury to saturation. When cool decant. This 
solution may be made in quantity and kept. II. Absolute alcohol. 
III. Chloroform-alcohol — chloroform and absolute alcohol mixed 
in equal parts. IY. Chloroform. V. Solid paraffin, melting-point 
46°-50° C. VI. Short wide-mouthed bottles. VII. Best cork stoppers, 
two for each bottle ; the one fitted with a piece of glass tubing 1 cm. in 
diameter and 3 cm. long. VIII. Number of glass rods drawn out into 
fine points, as one must avoid bringing metal instruments in contact 
with the picro-corrosive fluid. 
Method— A. The fixing and hardening of tissues. — Place tissue in at 
least fifty times its bulk of the picro-corrosive alcohol. Leave small 
objects (up to 1 cubic cm.) for twenty-four hours, larger objects for 
forty-eight hours and upwards in the fluid. Keep the bottle well 
corked. 
B. The replacement of the picro-corrosive alcohol by pure absolute 
alcohol. — 1. Pour off the hardening fluid till the tissue is just covered. 
Add absolute alcohol according to the size of the tissue in 1-10 drops 
every ten minutes, till the tissue is again in fifty times its bulk of fluid. 
After each addition move the bottle very gently to allow the added 
alcohol to mix with the hardening fluid. Leave tissue in this diluted 
mixture for twenty-four hours. In no case should this process be 
hurried, or strong diffusion currents will be set up, and the protoplasmic 
contents of the cell separate from the cell-wall. 2. Pour off the fluid 
till the tissue is just covered, and add absolute alcohol up to the original 
bulk. Move about the bottle gently every three or four hours. Most 
of the picro-corrosive material will thus be extracted after twenty-four 
hours. 3. Draw the fluid rapidly off by means of a pipette, and add 
absolute alcohol up to half of the original bulk. Any drying of the 
tissue must be carefully guarded against. Leave for twenty-four hours, 
and repeat the process. 
G. The replacement of the alcohol by chloroform. — 1. Pass, by 
means of a pipette, the chloroform-alcohol mixture to the bottom of 
the vessel, when the tissue will float on the mixture. Eemove then the 
superfluous alcohol by a pipette, leaving only enough to cover the 
tissue. 2. When the tissue has sunk in the chloroform-alcohol mixture, 
introduce by a pipette pure chloroform, on which the tissue will float ; 
the fluid above the tissue is removed by a pipette. After twenty-four 
hours the tissue may or may not have sunk in the chloroform ; if not, it 
may be induced to do so by heating the chloroform to 20° C. (not higher) ; 
if this fail, a little sulphuric ether may be added. After the tissue has 
sunk, leave for twenty-four hours. 3. Place a fresh supply of chloroform 
at the bottom of the vessel (50 times the bulk of the tissue), and if there 
is a distinct line of demarcation between the newly-added and the old 
chloroform, the upper layer should be removed by a pipette. 
D. The replacement of chloroform by paraffin. — 1. Place the tissue 
in a warm chamber heated to 25° C. ; add solid paraffin in pieces up to 
the size of a small pea. After each piece has dissolved, the bottle has 
to be moved about very gently to hasten the mixing of the paraffin, 
which will be in the upper layers, with the chloroform. Continue till 
no more paraffin dissolves. Tissue whicli did not sink in pure chloro- 
