154 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
On removal from the silver solution the pieces are placed in 96 per 
cent, spirit for fifteen to twenty minutes, and then for a quarter of an 
hour in absolute alcohol. The next step is to soak them in a dilute 
solution of celloidin for a quarter of an hour, then fix them to a piece of 
cork, after which they are hardened in 70 per cent, spirit, so that the 
sections may he cut about an hour after being removed from the silver 
solution. The sections are next immersed successively in alcohol and 
creosote, cleared up in oil of turpentine, and mounted in xylol-dammar. 
The dammar should be dried as quickly as possible by keeping the 
preparations in an incubator at 40° for twenty-four hours. 
Method for demonstrating Structure of the Cerebral Cortex.* — In 
his researches on the cerebral cortex, Prof. Ramon y Cajal used small 
mammals in the embryonic and recently-born conditions. The pro- 
cedure adopted was the rapid method of Golgi. The author found that 
the most favourable period for obtaining a good colouring of the 
nervous elements was not the same for all the animals employed ; for 
example, in mice the optimum varied from the 8th to the 25th or 30th 
day, while in the rabbit the favourable period was found to be from the 
1st to the 15th day after birth. The time required for hardening in 
the osmic-bichromate mixture was two, three, to five days, in recently- 
born rabbits, guinea-pigs, and cats, but this is only a rough estimate, 
for the time required varies for each animal and for every stage of 
development. This caution holds good not only for the fixation but 
also for the colouring of the different constituents of nervous matter, 
some elements requiring a longer time than others. 
In order to insure a certain result it was found necessary to always 
carry on the procedures at a constant temperature. In winter the 
author worked at a temperature of 25° to 26°, this being maintained by 
a stove with a thermo-regulator. 
The size of the pieces to be hardened should not exceed half a 
centimetre to a volume of 25 to 30 cubic centimetres of the mixture. 
Occasionally no reaction takes place or is very imperfect, owing 
to the proper period for impregnating having been exceeded. In this 
case a successful result may be sometimes obtained by reimmersing the 
preparations for another 24 or 36 hours in the silver solution. 
When colouring the superficial elements of the brain, it is very 
important to prevent any deposit of chromate of silver crystals on the 
surface. This may be avoided by the devices suggested by Martinotti 
and by Sehrwald, and also by leaving the pia mater and arachnoid on 
the cortex, or by covering the cortex with a thin layer of the fresh 
blood of the animal. 
The addition of one or two drops of a concentrated solution of 
chromic acid to the solution appears to aid the colouring of the col- 
lateral fibres. It is certainly advantageous in spinal cord, more 
especially if the vertebral column has to be cut together with the 
cord, since it helps to dissolve out the inorganic matter from the 
bone. 
The author used the original mixtures for the chrom-osmic acid 
and silver solutions, not modifying them in any way, nor did he adopt 
* La Cellule, vii. (1891) pp. 125-32 (3 pis., 19 figs.). 
