414 
stantly varying strains with every deviation of the long axis of the 
body from the normal. He further suggested that these variations in 
tension might act as stimuli upon the columnar cells of the sub- 
commissural organ, and that these might transmit the stimuli to appro- 
priate sensory and motor nerve cells in the brain and thence to the 
muscular system in such a way that the flexure of the body would 
be automatically regulated. 
IV. The Scope of the Investigation. 
Primarily, my experiments were directed towards solving the 
problem of the function of Reıssner’s fibre by the observation of 
living animals in which the continuity of that structure had been 
destroyed. 
A second object of the investigation was to obtain further in- 
formation upon the elasticity of the fibre in life. Hitherto, my atten- 
tion had been almost confined to a determination of the anatomical 
relations of the fibre and special precautions had been taken to pre- 
vent its displacement (cf. NıcHoLts, 1909). As a consequence I had 
obtained a recoil of the fibre, accidentally, in two or three cases only, 
where it had been cut before fixation was complete. The snarled 
condition had, however, been observed not infrequently in material 
which had not been specially prepared for the study of this structure, 
and in which the spinal cord had been cut previous to fixation. It 
was expected that a breaking of the fibre in the living condition would 
be followed by a withdrawal of the severed ends similar to that which 
had resulted from the cutting of the fibre in freshly killed material. 
Beyond the mere fact of the occurrence of such a recoil nothing had 
been recorded. It was hoped that the results of these experiments 
would decide the natural limits of this recoil, i. e., whether, when once 
started, the withdrawal of the fibre would continue until both free 
ends had retracted to their very points of attachment or whether, on 
the contrary, the tangle, always presuming that it were formed, might 
not operate automatically to check recoil by reaching such a size as 
to effectively block the lumen of the canalis centralis. Were this the 
case it might be expected to afford a temporary hold and perhaps to 
prevent the fibre from being put entirely out of action until the normal 
condition should once more be established by regeneration *). 
1) That regeneration does occur I had satisfied myself from an 
examination of sections through the regenerated tail of an Australian 
lizard (Pygopus sp.). These sections, which were kindly lent me by 
Professor J. P. Hit, were cut transversely at points in both the old 
