ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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freezing-point, and tlie explanation is, that tlie rapid congelation of the 
water interferes with the usual arrangement of the crystals, producing 
a wonderful series, which are entirely unlike any forms resulting from 
crystallization at the ordinary temperature. 
(3) Cutting-, including- Imbedding and Microtomes. 
Dextrin as an Imbedding Material for the Freezing Microtome.^ 
— Mr. T. L. Webb says that by taking an aqueous solution of carbolic 
acid (1 in 40) and dissolving therein sufficient dextrin to make a thick 
syrup, a medium is obtained which is superior to the time-honoured 
gum and sugar in three ways. It freezes so hard as to give a firm 
support without being too hard. It keeps better than gum. It is much 
cheaper, costing only 4d. a pound, whilst powdered gum acacia costs 5s. 
Dextrin dissolves but slowly in cold watei’, so that a gentle heat is 
advisable wlien making the mucilage. 
Imbedding in Celloidin.t — Dr. A. Florman recommends the follow- 
ing procedure for imbedding pieces of animal tissue in celloidin so as to 
obtain thin sections. After hardening the tissue in absolute alcohol, 
pieces about 3 mm. thick are placed for some hours in absolute alcohol, 
and after this in a test-tube containing a mixture of 3 parts ether and 
1 part alcohol. In a couple of days some celloidin solution is added 
until the mixture is about as thick as a thin syrup. Herein the pieces 
remain for 14 days or longer, when more celloidin is poured in to make 
a thicker solution. After 4-8 days the contents of the test-tube are 
turned into a shallow glass capsule, wherein the celloidin solution must 
form a layer of 10-12 mm. thick over the preparation. The pieces 
having been arranged in the desired position, the capsule is covered with 
a glass plate, a cover-glass being interposed so as to allow of slow 
evaporation of the celloidin solvent-^. In 2 or 3 days’ time a consistent 
mass free from air-bubbles is obtained, and from this the pieces are cut 
out so that each is surrounded by a layer of celloidin at least 3 cm. thick. 
When removed their under surface is to be daubed over with a thick 
solution of celloidin, so as to make all the surfaces of the same width. 
The y>ieces are replaced in the capsule to allow the new layer to become 
consolidated by evaporation of the ether and alcohol. Pieces thus pre- 
pared will have the consistence of cartilage, and sections from a block 
the sides of which are 1*5 cm. can bo made 0*015 mm. thick, and if 
the area of the surface be decreased, still thinner. 
Manipulation of Celloidin.^ — The failures that some microtomisfs 
experience when dealing with celloidin are due, says Dr. S. Apathy, to 
the neglect of a few slight artifices. Commercial celloidin in plates or 
in shavings should be first of all thoroughly dried in the air, whereby 
it is rendered hard, transparent, and yellowish. Pieces of celloidin 
thus hardened are put into an air-tight vessel and just covered with a 
mixture of equal parts of sulphuric ether and absolute alcohol. After 
having been allowed to stand for some time with frequent stirring, 
the supernatant fluid is decanted off. This may be called the original 
or No. 1 solution. Some of this, diluted with an equal volume of equal 
* The Microscope, ix. (1889) pp. 344-.5, from the ‘ National Druggist.’ 
t Zeitschr. f. AViss. Mikr., vi. (1889) pp. 184-0. J T. c., pp. 164-70 
1890. I 
