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conviction that a fibrillar structure is present but how this structure 
is to be regarded, that is the point respecting which we remain 
in uncertainty. 
There remains then only our last but at same time best resource 
and that is to try what information we can obtain from transverse 
and longitudinal sections tåken from preparations fixed, stained, and 
hardened in the best way our present histological technology can afford. 
As a very good method, for this purpose, I would especially 
recommend the following : the nerves or commissures, tåken directly 
from the living animal, are treatod with Flemmings fluid (chromo- 
aceto-osmic acid, strongest solution cmfr. p. 75 — 76) for 12 to 24 hours, 
then washed for some hours in running water, and stained with alum 
hæmatoxylin (Delafields formula), or in an aqueous solution of 
hæmatoxylin (0.5 ^ q), and afterwards treated with a solution of 
potassium-bichromate (0.5 — i %) as recommend by Heydenhain 
(vide p. 76). No w the structures are washed, again and hardened, 
somewhat quickly in alcohol gradatim. Preparations treated in this 
way can, as a rule, be very easily cut into thin sections, directly 
enclosed in paraffin only (vide p. 76). Embedding in celloidin or 
paraffin can of course also be employed; this can not, however, be 
performed with too great care as we have here to deal with struc- 
tures of the most delicate nature. 
In preparations carefully treated in this way, the nerve-tubes, 
with their contents, are fixed in their natural position and state, and 
no visible change of the form has tåken place. 
If we now examine good and thin longitudinal sections, it will 
already, under low powers of the microscope, be easy to observe 
a distinct longitudinal striation in the larger as well as the smaller 
nerve-tubes. The extremely slender longitudinal lines or »fibrillæ« 
have got a distinct blackish staining, and are situated with intervals 
between them, just similar to what we have found in the fresh state. 
The substance in these intervals is not stained, and has a homogeneous 
or rather a slightly granular appearance. If now, however, the 
stained fibrillæ are real fibrillæ swimming in this homogeneous un- 
stained substance, it is evident that they, in thin transverse sections 
of nerve-tubes, must appear as minute black dots or points, just 
similar to what, ViGNAL for instance, has also really described and 
illustrated. 
But what do we hnd} — Instead of hlacJc dots, tve find in the 
sections of the tubes a delicate reticulation, ivith minute circular 
meshes, apparently formed hy extremely slender filaments (fig. 2; fig. 5, t). 
