THE FUNCTION OF REISSNER’S FIBER iy gl 
of the fiber, provided material which throws considerable light 
upon the recoil of the fiber. 
A general account has been given above of the condition of 
Reissner’s fiber in the hinder part of the spinal cord of this speci- 
men. From that description it will be apparent that, since both 
before and behind the incision the fiber extends actually to the 
severed ends of the filum terminale (text-fig. 4), there could 
have been no retraction of the fiber as a sequel to the opera- 
tion. Nevertheless, in the condition of the fiber, both in front 
and behind the point where it was broken by the operation, 
there is very distinct evidence of a recent retraction. 
In the terminal (severed) portion of the terminal filament 
(text-fig. 4a) the fiber is seen to be considerably swollen, the 
swelling becoming more pronounced in the terminal sinus where 
the fiber passes into a loose spiral; the terminal plug is not recog- 
nizable, having collapsed, presumably, when the recoil began. 
Immediately in front of the incision (text-fig. 4b) the fiber is 
found in a wonderfully twisted state and continues markedly 
coiled to the forward end of the piece of tissue examined. The 
torsion is not uniform, short simply-twisted stretches interven- 
ing between greatly convoluted lengths of fiber.. As already 
pointed out, this short length of terminal filament contains very 
many times its length of Reissner’s fiber. It is obvious, then, 
that not only must this retraction have been due to a withdrawal 
of the fiber from before backwards but, also, that it must have 
been in progress prior to the operation, since otherwise it could 
not have affected the severed piece of fiber in the region behind 
the experimental lesion. 
The incipient coiling of the fiber behind the incision is evidence 
that retraction had been in progress but for a very short time 
when the experimental incision separated this terminal portion 
of the fiber and, as it happened, checked further recoil behind 
this point. In front of the lesion, however, a gradual retrac- 
tion continued during the 3 hours while the specimen lay mo- 
tionless,? until a great length of Reissner’s fiber had accumu- 
lated in the hinder part of the spinal cord. 
3 Doubtless the retraction actually continued until finally BueBE Ce by. the 
hardening action of the fixing fluid. 
