322 ME. J. L. CLAEKE ON THE INTIMATE STEUCTUEE OF THE BEAIN. 
that evaporates from their upper surfaces. In a short time, sometimes almost immedi- 
ately, they will become quite or nearly transparent, when they are to he removed to glass 
slides on which a little Canada balsam has been dropped. Before they be finally 
covered with thin glass they should be examined under the microscope, and if all their 
parts be not perfectly transparent or distinct and well defined, a little turpentine and 
Canada balsam should be alternately dropped on them from time to time until the 
requisite effect be produced. If the sections be thick, I find it best, instead of floating 
them on the turpentine, to place them in a shallow vessel the bottom of which is simply 
wet with turpentine, which then ascends from below while the spirit evaporates from 
above. Before using the turpentine I also frequently remove a large portion of the 
spirit by placing the sections for a minute on fine blotting-paper. The process may be 
further hastened by the following plan : place the section on a glass slide, after the 
spirit has been partially removed by blotting-paper ; drop on it some turpentine, and 
then tap it gently with the end of the finger, repeating these steps alternately until 
transparency be produced. 
By any one practised in this method, a thin section, after having been coloured, washed, 
and steeped in the strongest spirit, may be rendered perfectly transparent and fit for 
mounting in Canada balsam in the course of eight or ten minutes ; and a section of mo- 
derate thickness in fifteen minutes. But many observers have complained that the use 
of turpentine renders the process slow, and they have therefore substituted for turpentine 
a variety of other media, as oil of cloves, creosote, carbolic acid, which so much resembles 
it, &c. Creosote is that which is now most used on the Continent. In this country 
another modification of my method has been introduced by Dr. Charlton Bastian. The 
section having been coloured, washed, and saturated in spirit, is placed on a drop of 
carbolic acid, instead of turpentine, in the centre of a glass slide. In less than two mi- 
nutes it is rendered transparent ; and when this is accomplished (having got rid of any 
excess of carbolic acid), he pours over it three or four drops of chloroform, in which the 
specimen is allowed to remain for two minutes. The superfluous chloroform is then 
poured off, whilst one or two drops of a solution of Canada balsam in chloroform are 
dropped over the specimen, and the covering glass is then quickly applied. The whole 
process extends over ten minutes*. Although these modifications may possess some 
advantages in point of expedition, the principle is the same as that of the original 
method which I introduced. The preparations so made are certainly not in the slightest 
degree superior to my own. 
Gerlach now hardens the cord in a solution of bichromate of ammonia of the strength 
of one to two per cent. The sections are then put into a solution of 1 part of chloride 
* Journal of Anatomy and Physiology, November 1867. Dr. Bastian here speaks of my original process 
•with turpentine extending over a space of four or five hours ! If this were the case it would have been impos- 
sible for me to make the thousands of preparations I have made, and to have done the work I have done by 
means of them. However, for Dr. Bastian’s satisfaction, I rendered a section transparent, and fit for mounting 
in Canada balsam, in his presence, in the course of fifteen minutes. 
