THE FUNCTION OF REISSNER’S FIBER 119 
nervous system. Accordingly, there will be need, at this time, 
only for a brief review of the various suggestions which have 
been put forward as to the nature and function of the fiber and 
a short account of the present state of our knowledge of the fiber 
and its connections, the reader being referred to the above men- 
tioned work for further details. 
I gladly avail myself of this opportunity to express my nee 
to Professor Dendy for valuable advice and criticism throughout 
the progress of the work: also, to the Government Grant Commit- 
tee of the Royal Society, for Grants in Aid; to the British Asso- 
ciation for the Advancement of Science and the Senate of the 
University of London for placing at my disposal their tables at 
the Plymouth Marine Laboratory, and to Dr. Allen, Director of 
the Laboratory, for the facilities afforded me in the prosecution 
of the research. 
I. INTRODUCTION 
A. A review of the suggestions which have been made concerning 
the nature and function of Reissner’s fiber and the 
sub-commissural organ 
1. Reissner (’60), by whom the fiber which now bears his name 
was discovered, believed that this ‘Centralfaden’ was simply a 
nerve fiber and to him, therefore, it was remarkable principally 
on account of its peculiar situation. He found it, as is well 
known, lying freely as an axial thread in the central canal of the 
spinal cord of the lamprey. Since the diameter of the fiber in 
this animal (in which alone he had observed it) is, approxi- 
mately, that of a moderately coarse nerve fiber, it is scarcely 
surprising that, its unusual situation notwithstanding, Reissner 
came to this conclusion. Kutschin (’63) who confirmed Reiss- 
ner’s discovery, accepted that author’s view of its nature. 
Neither of these observers was able to trace the fiber into the 
brain ventricles and they believed it to be confined to the cen- 
tral canal of the spinal cord. 
2. That a nerve fiber should occur in such a situation seemed 
to Stieda (’68, ’73) altogether improbable and he decided that 
Reissner’s fiber (‘jenen riithselhaften Strang’) must be an arti- 
