THE FUNCTION OF. REISSNER’S FIBER 187 
Whether the delicate fiber found extending backward slackly 
in some specimens (46, 55) almost to the region of the incision, 
is to be regarded as yet another early stage in regeneration is less 
certain. Possibly it is a backward growth from the free end of 
the fiber in a snarl which has altogether failed to become dis- 
entangled. On the other hand the fineness of the fiber may be 
nothing but an individual peculiarity. 
It is noteworthy that, where this abnormally fine fiber was 
found, it had retracted but little when cut and the oe 
reaction had proved to be but slight. 
In view of the fact that a case of complete repair had been 
obtained in but a single experiment (2), it has not been possible 
to determine the period within which regeneration might nor- 
mally be expected to take place. If the incision has completely 
divided the filum terminale (in practice an inevitable conse- 
quence of any attempt to cut the fiber) even though this be very 
far posteriorly, it is almost certain that regeneration cannot be 
effected until a new (secondary) sinus terminalis has been formed. 
It is unlikely that this comes into existence earlier than the end 
of the second week, although the exact time would depend upon 
the regenerative powers of the tissue of the individual and would 
be likely to take place more quickly in young and rapidly grow- 
ing specimens. The new attachment of the fiber may, however, 
be even then delayed if the retraction has been very consider- 
able, has resulted in a tangled knot, or if the fiber has broken 
very far forward. 
In several of my experiments the fiber had returned nearly 
to its normal diameter and had pushed backwards to the region 
of the incision within a week of the operation, while the spiral 
twist appears to be straightened out during the second day under 
ordinary circumstances. A complicated tangle evidently re- 
quires a considerable period in which to become resolved and 
in such a knot it is probable that the spiral twisting may per- 
sist rather longer. In my experiments, however, only a short 
length of the fiber was actually separated and consequently no 
great length of new growth, if any, was required to enable the 
fiber to extend to the newly formed sinus terminalis. Where, 
