35 
one must acknowledge that the chemical composition of the cerebro- 
spinal fluid was the same, or nearly the same, as the substance which 
forms the axis cylinders. In regard to its origin and ending REISSNER 
could find nothing and he knew of its occurrence in the cord of Pe- 
tromyzon only. 
KutscHhin (°63) confirmed ReIssNer’s discovery in Petromyzon, 
naming the structure Reıssner’s fibre, but failed to add anything to 
his knowledge of it. 
StrepA (68) found Reıssner’s fibre present in all Teleosts ex- 
amined by him. He describes it as a cylindrical rod of homogeneous 
structure, having in general a diameter of 3,8 uw. STIEDA considered 
to be an artifact produced by the chromic acid used in fixation. 
SANDERS (’78) described the occasional occurrence of a rod in the 
canalis centralis of Mugil, and agreed with Sriepa in believing it to 
be “the coagulated liquid contained therein”. 
SANDERS (’86) failed to find the rod or fibre in Plagiostomes, 
but says (86, p. 740): “There is often found a small quantity of gra- 
nular matter in the canalis centralis, which presents a granular appear- 
ance after coagulation; it corresponds to the rod occasionally found in 
the canalis centralis in the Teleostei and shows perhaps that the cerebro- 
spinal fluid coagulates more firmly in the latter than in the former”. 
SANDERS (94) again found this structure of conspicuous size in Myxine. 
If REISSNER’s fibre has been seen by later investigators, SANDERS’S view 
has probably been accepted by them, as I find no further reference 
to this structure in later literature. 
In spite of the convincing clearness and uniformity of this fibre 
in the preparations where it was first seen, its unusual position made me 
at first incredulous as to its preformed organic nature. My first care 
therefore was to make certain that it was in no way due to the parti- 
cular fixing agent used, either in forming artifacts or in coagulating 
the cerebro-spinal fluid. 
It was first observed, as already stated, in the trout, which had 
been fixed in corrosive sublimate. Knowing the proneness of corro- 
sive sublimate to form artifacts closely resembling organic structures, 
I searched for the fibre in material fixed in fluids containing no corro- 
sive sublimate. It was found equally clear and sharp in material fixed 
in FLemMina’s fluid, in formol and in many other fluids equally unlike 
corresive sublimate in their action. 
The fixing fluids used were chosen so as to secure as great a 
diversity of composition as possible, in order to test the whole range 
of possible effects on the coagulation of fluids in the canalis centralis 
3* 
