128 GEORGE E. NICHOLLS 
actual condition of the fiber figured was due to its rupture in 
removing the central nervous system from the body for pres- 
ervation. The appearances are those which would be observed 
if the fiber were broken accidentally in the hindbrain and in the 
region of the filum terminale by section of the nervous system 
in those regions, or by handling during dissection. 
From the figures it would appear that there may have been a 
somewhat considerable local disturbance of the central nervous 
system in consequence of the experiment. While this might 
have obscured, to some extent, the reaction consequent upon the 
breaking of the fiber (especially as a point’very far forward was 
selected for the operation) it is nevertheless much to be regretted 
that nothing is recorded as to the behavior of the living animals 
as the result of the experiments. 
C. An account of the present state of our knowledge of Reissner’s 
fiber 
Reissner’s fiber is an extremely delicate. protoplasmic thread, 
having, in general, a diameter of more than 1y and less than 3un. 
It possesses a high refractivity and, in the normal tense con- 
dition, appears to be absolutely structureless. 
It is normally present in the central nervous system of practi- 
cally all vertebrates and may be seen, most readily, in longi- 
tudinal (sagittal) sections of the spinal cord. It is necessary, 
however, that the nervous system shall have been preserved 
entire and immediately after the death of the animal; even then, 
carelessness in handling during the dissection may cause the 
fiber to snap, or it may chance that the fiber was broken prior 
to the death of the animal. Generally, however, if the central 
nervous system has escaped damage, Reissner’s fiber will be 
found everywhere in the central canal stretched taut and lying 
centrally in the canal. It maintains a uniform thickness and 
shows no trace of spiral winding. At frequent intervals it 
appears to be connected with the ependymal epithelial cells by 
delicate cilia-like protoplasmic filaments (figs. 29, 30). 
