ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
689 
The author deals at length with this portion of his subject, and 
shows how the Microscope has assisted in the attempt to determine the 
history and mutual relation of these rocks. One of the most important 
results within the last few years has been the demonstration that 
without exception these crystalline schists are very old, all probably 
older than the first rocks in which traces of life have been found. The 
conclusion at present arrived at is that “ the environment necessary for 
changing an ordinary sediment into a crystalline schist existed generally 
only in the earliest ages, and but very rarely and locally, if ever, since 
Palaeozoic time began.” 
The crystalline schists then are the relics still preserved to us of 
the early days of this earth’s history when the temperature near the 
surface was still very high. Since that time the zone for marked 
mineralogical changes has been continually sinking until at the present 
day it has reached a depth practically unattainable. “ The subterranean 
laboratory still exists, but the way to it was virtually closed at a com- 
paratively early period in the earth’s history.” 
In conclusion the author considers that the progress made since the 
Microscope was pressed into the service of geology augurs well for the 
future, and inspires the hope that we shall at last learn something of 
the history of the earliest ages “ when the earth had but lately ceased to 
glow, and when the mystery of life began.” 
j8. Technique.* 
Microtechnique of Vegetable Objects.! — Dr. L. Klein describes 
at length some points in the technique of vegetable histology, and con- 
siders them under the heads of imbedding in celloidin and paraffin, the 
media suitable for mounting, and the most convenient staining solutions. 
For celloidin imbedding, the object having been thoroughly dehy- 
drated by immersion in absolute alcohol in a Schulze’s dialyser, is 
soaked for 6-10 hours in a mixture of equal parts of ether and absolute 
alcohol. The piece, the sides of which should not exceed 3-5 mm. long, 
is then placed in a thin solution of celloidin (about 5 per cent.) in equal 
parts of ether and absolute alcohol. In this solution, contained in tightly 
stoppered bottles, the object remains for at least three days. After this 
time the celloidin solution is thickened by slow evaporation of its 
solvents, and this is effected first by substituting a cork for the glass 
stopper, and afterwards by inserting strips of paper between the neck of 
the bottle and the stopper. It is finally inspissated by direct evapora- 
tion, and then by immersion in 60 per cent, spirit. The celloidin block, 
the section surface of which should not exceed a square centimetre, is 
fixed on cork or wood by means of a thin layer of celloidin solution of 
the consistence of syrup. 
The surface of both the cork and section block should be previously 
moistened with ether, and the two parts having been tightly squeezed 
together, the mass will be sufficiently adherent in 10-15 minutes for 
* This subdivision contains (1) Collecting Objects, including Culture Pro- 
cesses; (2) Preparing Objects; (8) Cutting, including Imbedding and Microtomes; 
(4) Staining and Injecting; (5) Mounting, including slides, preservative fluids, &c. ; 
(6) Miscellaneous. 
f Jahrbiicher f. Wiss. Botanik (Pringsheim), xxiv. (1892) pp. 1-57. 
1892. 3 a 
