608 
MR. J. L. CLARKE’S RESEARCHES INTO 
first by reflected light with low magnifying powers, and then by transmitted light 
with higher ones. 
According to the second method, the section is first macerated for an hour or two 
in the mixture of acetic acid and spirit. It is then removed into pure spirit, and 
allowed to remain there for about the same space of time. From the spirit it is trans- 
ferred to oil of turpentine, which expels the spirit in the form of opake globules, and 
shortly (sometimes immediately) renders the section perfectly transparent. The pre- 
paration is then put up in Canada balsam and covered with thin glass. By this 
means the nerve-fibrils and vesicles become so beautifully distinct that they may be 
clearly seen with the highest powers of the micoscope. If the section be removed 
from the turpentine when it is only semi-transparent, we sometimes obtain a good 
view of the arrangement of the blood-vessels*. 
All the observations described in this paper were made and verified also on sec- 
tions in a perfectly fresh state and unaffected by any chemical re-agent ; and when- 
ever it was proposed to examine the natural structure of any particular part, as the 
nerves and vesicles, a specimen was selected from an animal immediately after 
death. 
The drawings have been executed by myself with the greatest care, and may be 
relied on as faithful and exact delineations of what was seen under the microscope. 
The outlines of all were taken by means of a camera lucida, in order to ensure cor- 
rectness. 
Of the Gy'ey Substance of the Spinal Chord. 
At the lower end of the spinal chord the posterior grey substance consists only of a 
single mass, having a broad and rounded extremity, and formed, as we shall presently 
see, by the coalescence of the two posterior cornua along their inner borders, where, 
being increased in breadth, they meet each other in the middle line (see Plate XX. 
fig. 1). In consequence of this arrangement, the substantia gelatinosa extends unin- 
terruptedly and horizontally across from one side to the other. From the posterior 
white columns it is separated, particularly on each side, by a kind of border com- 
posed of fine nerve-tubes, which wind round it and proceed from the posterior roots 
of the nerves. 
The anterior grey substance, on the other hand, is here, as in other regions of the 
chord, separated by the anterior white columns into two cornua of considerable size. 
These curve somewhat inwards, taper to an irregularly rounded point, and nearly 
reach the circumference of the chord. 
Here also the spinal canal is very distinct and large, being the x^th part of an 
* This mode of preparation succeeds best in cold weather ; for in summer, the chord, however fresh when 
immersed in the spirit, remains more or less spongy, instead of becoming firm and dense in the course of five 
or six davs. The spirit should be diluted with an equal quantity of water during the first day, after which it 
should be used pure. Certain modifications of this mode of preparation may be sometimes employed with ad- 
vantage by a practised hand. 
