274 
NOTES AND MEMORANDA. 
tlie many important phenomena which may he explained by the study 
of pedesis, and I propose to follow up the investigation of this move- 
ment in regard to the several substances which tend to increase it.” 
The Pi-eparation of Thin Sections of Objects of different Consistency, 
— In investigating the anatomy of corals Mr. G. von Koch, of 
Darmstadt found the calcareous skeleton one of the greatest drawbacks 
to his researches, as it often prevented any observations of the struc- 
ture of these animals. Sections of decalcified pieces give good results 
only in special cases. Generally the decalcifying and still more the 
succeeding operations so disarrange the separate parts that their 
original relative positions can scarcely be recognized, and the structure 
of the calcareous parts is of course entirely lost. He applied the 
following method to overcome the difficulties, and obtained prepara- 
tions that would show very clearly the structure, form, and position 
of the different elements. Pieces as small as possible of the object 
to be cut are stained thoroughly, and after rinsing, all water is got 
rid of by means of weak and afterwards proof alcohol. The pieces 
are then put in a cup filled with a very thin solution of copal in 
chloroform. (This is easily made as follows : — Pound the coarse 
pieces of broken copal in a mortar with fine sand, pour chloroform 
over the fine pow^der thus obtained, and filter the solution.) Then 
slowly evaporate the copal solution by putting the cup on a piece 
of pottery ware, which is warmed by a common night-light. The 
slower the evaporation the better. When the solution can be drawn 
up in threads wffiich become brittle on cooling, the pieces are taken 
out of the cup, aud laid for some days on the ware to harden quicker. 
When they have become so hard that the edge of the finger-nails 
makes no impression, cut the pieces into thin sections with a saw, and 
grind them smooth and flat on an ordinary sharpening stone. Then 
cement the plates by their smooth sides to a slide by means of Canada 
balsam or copal varnish, and lay them again on the warm plate. 
After some days, when the preparation has become firmly fixed, grind 
it first on a revolving grindstone (or a flat one), and then on a sharpen- 
ing stone until the section has acquired the right thinness. Wash 
the section well w ith water and add Canada balsam, and cover with a 
covering glass. 
If it is desired to show small quantities of organized substances 
in calcified tissues, the- section is treated as above; but before the 
covering glass is put on it, it should be placed in chloroform till all 
the resin is drawm out, then carefully decalcified, and last of all 
coloured. The organic parts can be represented still more beautifully 
and without the least change of position if the section, as described 
above, is freed of resin, then cemented with very thick Canada balsam 
to a slide, and the exposed half only carefully decalcified, then washed 
and stained. By this means he succeeded in showing, for example, the 
most delicate connective-substance-lamellsB in the skeleton of Isis 
elongata.* 
Measurement of the Dihedral Angles of Microscopic Crystals . — 
M. Em. Bertrand, whose paper on this subject, presented to theErench 
* ‘ Zoologischer Anzeiger,’ vol. i. p. 36. 
