THE LUMBAR ENLARGEMENT OF THE SPINAL CORD. 951 
11. That the posterior roots are connected by curved fibres or bundles of fibres, pro- 
ceeding from one root and curving round after penetrating the gray substance, becom- 
ing connected with some other root above or below. The same is seen in transverse 
sections with regard to roots situated side by side, both anterior and posterior, the 
looping fibres sometimes proceeding directly from root to root, and sometimes passing 
through cells. ! 
From which it results that the same fibre must in different parts of its course con- 
duct both centrifugally and centripetally. 
12. That, besides the looped recurrent fibres, the three principal courses taken by the 
posterior roots before entering the gray substance are with reference to a longitudinal 
plane, ascending oblique, descending oblique and transverse. 
The method of preparation usually employed was a modification of Gerlach’s and 
Clarke's, although many others were employed, according to the object in view. The 
following method gave the best results from which to make drawings. Thin sections 
from the cord, hardened in alcohol, were washed a few minutes in pure water, and then 
immersed in glycerine, to which Gerlach's solution of carmine,* previously filtered, had 
been added; in this the sections were allowed to remain four to eight hours, according 
to the tint desired (a light tint interfering least with the details and sharpness of out. 
line). I have been able to obtain more delicately colored specimens and more clearly 
defined structure by the use of glycerine than by any other method. The sections are 
then washed first in pure water, afterwards with strong alcohol, in which they are 
allowed to remain about an hour, and are now ready for preparation with turpentine, 
according to Clarke's method; they may be put up in Canada balsam, or, as I have 
found very advantageous, in thick, colorless copal-varnish, which often preserves 
minute details better than balsam. Although Stilling and others have found much 
- fault with Clarke's method of preparation, on account of the too great transparency it 
sometimes gives, I am convinced that, with practice and some slight modifications, it 
is the only one suited to the minute study of the cord, other methods seeming to me, 
after thorough trial, quite unsatisfactory as compared with Clarke's. As a hardening 
material I have often employed chromic acid with considerable advantage; but when 
coloring-matter is used, alcohol is most suitable, and is certainly much easier to suc- 
ceed with. 
* Gerlach, Mikroskopische Studien, Erlangen, 1858. Solution of carmine in water, to which a few drops 
of strong ammonia have been added. 
