THE FUNCTION OF REISSNER’S FIBER 127 
In his figure 10, Reissner’s fiber is seen in transverse section, 
occupying quite an appreciable part of the lumen of the central 
eanal. As it is traced backwards from this level (the first cervi- 
cal segment) through the third cervical segment (fig. 9) towards 
the point of lesion in the fifth cervical segment (fig. 8), it is seen 
to constantly diminish in size. Behind the point of lesion this 
diminution in size continues as will be seen in figures 11 and 12 
but, more caudally, the diameter of the fiber is again seen to 
increase (fig. 13), this latter figure representing a section through 
the spinal cord in the lumbar region. 
Now this is not at all what one would expect to find where 
Reissner’s fiber had been broken experimentally. Usually it 
would be found that on either side of the lesion there was a 
stretch of canal devoid of fiber. Still further from the lesion 
the severed ends of the fiber might be found swollen and perhaps 
knotted if the material were killed and fixed soon after the lesion 
had been made. ‘Tracing the fiber distally, in either direction, 
from these knotted or swollen ends one would expect to find that 
the fiber diminishes in diameter until the normal size is reached. 
If, however, the killing of the material were postponed for a 
considerable time after the experimental operation the swollen 
end and the spiral twisting would have disappeared and the 
fiber-would have straightened out backwards, extending practi- 
cally to the point of lesion, nearly normal except that it might 
not have regained its taut condition. The piece lying posterior 
to the lesion might have retracted wholly backwards to the 
end of the cord. If the material were not killed until several 
weeks after the operation it is probable that regeneration would 
have largely re-established the normal condition throughout. 
The condition figured by Horsley, in which the fiber is most 
swollen anteriorly, regularly diminishes in diameter towards 
and past the lesion (and probably becomes normal in the thoracic 
region) but shows a renewed swelling very far back, suggests 
that the condition of the fiber may have had nothing to do with 
the actual experiment. I should judge that sufficient time had 
elapsed after the experiment to permit of regeneration, and the 
