NS 4 GEORGE E. NICHOLLS 
fiber has been broken and depends, possibly, upon the size of the 
central canal in that particular region for, in the case of a sud- 
den recoil, the spiral winding may produce at or near the severed 
end a mass of coiled fiber which apparently checks further re- 
traction. With the retreating end of the fiber may be dragged 
numerous epithelial cells and, around it, will collect a quantity 
of coagulum (fig. 17) which may render it difficult to distinguish 
exactly the condition of the knotted end. 
On the side of the tangle remote from the point of section, the 
fiber usually emerges as a coiled thread and thence passes gradu- 
ally into a more open spiral. If the fiber has been cut at a 
sufficient distance from its attachment, this open spiral may pass 
into a swollen but straight stretch and ultimately be found to 
pass almost or quite into the normal condition. Broken, how- 
ever, near to one of its attachments, the fiber will almost cer- 
tainly withdraw violently and completely to that attachment, 
from which it may even tear itself free, dragging with it many 
of the epithelial cells. 
While this retraction which is so characteristic of Reissner’s 
fiber is, as I have pointed out (’09), altogether unlike anything 
known in a nerve, neither does it altogether resemble the recoil 
of a simple (homogeneous) elastic thread. It is, therefore, of 
especial interest that I have been able, recently, to detect in a 
greatly swollen and retracted fiber what appears to be a fine 
deeply staining central axis (fig. 17); the resemblance of the fiber 
to the stalk of a Vorticella (with which I have already compared 
it, 712 a, p. 25) is thereby greatly enhanced. ‘This appearance 
is somewhat inconstant and never to be made out in the unrelaxed 
condition. 
I have been unable to decide whether the numerous delicate 
fibrillae (fig. 29) seen in the central canal of the spinal cord are 
in organic continuity with Reissner’s fiber or whether they are 
merely unusually long cilia which have been cemented to the 
fiber after death by the coagulated cerebro-spinal fluid. That 
the former view is probably correct is indicated, I believe, by 
the fact that in the cases in which some retraction of the fiber 
has occurred it is very rare to find any of these fibrillae apparently 
