374 BOTANICAL GAZETTE [MAY 
tissues from coagulating a film of collodion on the outer surface which 
would interfere with infiltration. -The objects may remain in the 2 per 
cent. collodion for twenty-four hours to several days or weeks at pleas- 
ure. The 2 per cent. is decanted, and the 5 per cent. poured on, 
which also may remain for twenty-four hours or more. Care should 
be used to prevent evaporation in the storage bottles of collodion, or in 
the vials during infiltration. After replacing the corks the bottles can 
be inverted for a moment, and the collodion running around the cork 
seals it. The objects are now poured with the 5 per cent. collodion 
into shallow paper boxes, the latter being received into vessels ordi- 
narily employed as moist chambers, though there should be no water in 
the chambers. Here they are allowed to remain for two days or so 
while the collodion slowly thickens to the desired consistency, when 
the boxes are immersed in 95 per cent. alcohol for about twenty-four 
hours. The paper is now stripped from the block of collodion, and 
the latter is stored in 80 per cent. alcohol. 
The paper trays should be lubricated previously on the inside with 
vaseline so that the paper will easily part from the collodion. The 
vessel used for a moist chamber should be one which can be partly 
opened at the top, never at the bottom, for the circulation of air, s0 
that the thickening of the collodion will not be unnecessarily pro- 
longed, and at the same time it must be slow enough to permit all air 
bubbles, which may be present when the material is poured in the 
trays, to rise to the upper surface and disappear, and also to permit 
an even thickening of the collodion lest an outer layer is hardened 
quickly which prevents the proper hardening of the interior. The 
trays should be of such depth that they may be filled at once with an 
amount of collodion which when thickened will be of the desired 
thickness for sectioning. I usually employ trays from 1o to ! ~ 
deep. If there is not sufficient 5 per cent. collodion in the vial at oe: 
time to fill the tray more is added. The trays vary in size according — a 
to the amount of material to be imbedded, and frequently several trays = 
are used for one lot of material. The trays may vary from 5-10™ long — 
by 3-8™ in width. As soon as they are filled with the collodion @ 
small needle is employed to adjust the objects in convenient position 
for orienting, and at such distances that each may be cut out i” : : 
block of hardened collodion of such a size as to fit directly in the }4¥° 
of the microtome. It thus requires but little time to place the materi” — 
in the trays in the nearly closed receptacles where evaporation may 8° 
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