MR. J. L. CLARKE ON THE INTIMATE STRUCTURE OE THE BRAIN. 
321 
structure supplied by tbe anatomist. From a want of this information serious blunders 
have been frequently made ; for in dividing even a small part, particularly of the medulla 
oblongata, the operator may injure other parts, with which, as we have abundantly seen, 
it is so closely connected. Lorry and Serres divided the medulla oblongata through 
the olivary bodies, and the latter anatomist concluded that the instant death of the 
animal was due to injury of those bodies; but if he had known that he had cut through 
the nucleus of the vagus, which Stilling had the merit of pointing out, his conclusion 
would of course have been different. On the other hand, the anatomist should make 
himself acquainted with the labours of the experimentalist, and pursue his researches by 
the light which they afford. It is in this way that observation, experiment, and induction 
alternately enlarge or enlighten the field of research and point out each other’s path. 
Appendix (added during the printing of the Paper). 
On the Method of making the Preparations. 
The method which I introduced some years back (1851) for rendering sections of the 
brain and spinal cord transparent and preserving them in Canada balsam, has been 
generally adopted both in Europe and America. The principle of the method is this : 
given a section of opake nervous substance that has been hardened in a fluid not mis- 
cible with Canada balsam ; to render that section transparent and permeable by Canada 
balsam without drying it. One of the fluids which I employed in the process was oil 
of turpentine. The whole process may be described as follows. 
The spinal cord or medulla oblongata is to be cut into pieces of from half an inch to 
an inch long and hardened in a solution of chromic acid, composed of one part of the 
crystallized acid to two or three hundred parts of water'*. To this solution I generally 
add a small quantity of bichromate of potash, which brings out the nuclei of the nerve- 
cells more distinctly, and causes the grey substance to take the colour of carmine more 
brightly. At the end of three or four weeks the medulla is in a condition fit for making 
thin sections by means of a razor or other sharp knife wet with spirit of wine. If the 
sections are to be coloured with carmine, the ammoniated solution of this substance 
should be previously filtered, and the sections should be washed free from the spirit 
used in cutting them, before they are placed in the carmine solution, for spirit readily 
precipitates the carmine in the form of granules. When sufficiently coloured the sec- 
tions should be again washed in water, and then soaked in strong spirit for a few minutes 
to expel the water. Sometimes a few drops of acetic acid may be added with advan- 
tage f. On removing them from the spirit, the sections, if thin, are to be floated on the 
surface of pure oil of turpentine, which will ascend from below and replace the spirit 
* Tor the convolutions of the cerebrum and cerebellum the solution must be much weaker. 
f Mr... Adam Addison; late of the Montrose Royal Asylum, sometimes adds a few drops of a saturated spiri- 
tuous solution of chloride of sodium instead of acetic acid. 
2 y 2 
