THE FUNCTION OF REISSNER’S FIBER 179 
The less noticeable reaction which I have recorded of so many 
of my specimens (viz.: the departure of the long axis of the body 
from the normal position in repose) was very probably exhibited 
by Sargent’s specimens, also, when at rest. This, however, 
would be little likely to attract the attention of an observer who 
was viewing the specimens (whether confined in the cage or 
free in the pool) from above as they must of necessity have 
been viewed. 
Such evidence, then, as is available suggests that the nearer 
the break in the fiber is to the sub-commissural organ, the more 
pronounced is the reaction. On the other hand, there is a 
marked reaction in many cases in which there has been no appar- 
ent interference with the taut condition of the fiber in the ante- 
rior part of the spinal cord and brain and in which, therefore, it 
might be supposed that the sub-commissural organ is little if at 
all affected. 
While, therefore, I am inclined to agree with Tretjakoff (13) 
in assigning a considerable importance to the detached sensory 
cells distributed along the entire length of the central canal (and 
possibly also in the isthmic canal), I think that there can be 
little doubt concerning the supreme importance of the sub- 
commissural organ as the center of this sensory apparatus. 
That Dendy’s suggestion of the manner in which the stimulus 
may be supposed to be brought to bear upon its related sensory 
cells by alterations in the tension of the fiber is much more prob- 
able than Tretjakoff’s view that the stimulus is a result of pres- 
sure of the fiber upon sensory cells admits in my mind, of little 
doubt. As already pointed out, I believe that Tretjakoff’s 
statements upon this point are based upon a study of material 
in which a retraction of the fiber had taken place and in which, 
therefore, the normal anatomical relations of the fiber are not 
seen. I interpret the ‘knobbed ends’ of the sensory processes 
as the remains of the broken fibrillae (which had connected 
Reissner’s fiber with the sensory cells in the ependymal epi- 
thelium of the canalis centralis) retracted to the parent cells. 
