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THE CEREBRO-SPINAL SYSTEM OF NERVES. 627 
These facts have been established by a few simple but im- 
portant physiological experiments, which will now be briefly 
described: 1. Stimulation of the peripheral end of a spinal 
nerve gives rise to muscular movements; while stimulation of 
its central end causes pain. 2. Upon section of the anterior 
root, stimulation of its central end gives negative results; but 
of its peripheral end causes muscular movements. 3. After 
section of the posterior root, stimulation of the distal end is 
followed by no sensory or motor effects; of its central end, by 
sensory effects (pain). 
These experiments show clearly that the anterior roots are 
motor, the posterior sensory, and the main trunk of the nerve 
made up of mixed motor and sensory fibers. 
Exception.—It has been found that sometimes stimulation of 
the peripheral end of the anterior root has given rise to pain, 
an effect which disappears if the posterior root be cut. From 
this it is inferred that certain sensory fibers turn up.into the 
anterior root a certain distance. Such are termed “recurrent 
sensory fibers.” 
Additional Experiments—1. It is found that if the anterior 
root be cut, the fibers below the point of section degenerate, 
while those above it do not. 2.-On the other hand, when the 
posterior root is divided above the ganglion, the fibers toward 
the cord degenerate, while those on either side of the ganglion 
do not. From these experiments it is inferred that the cells of 
the posterior ganglion are essential to the nutrition of the sen- 
sory fibers, and those of the anterior horn of the cord to the 
motor fibers. 
Pathological —_Pathology teaches the same lesson, for it is 
observed that, when there is disease of the anterior gray 
cornua, degeneration of motor fibers is almost sure to follow. 
These cells, whether in the ganglion or the anterior horn, have 
been termed “trophic.” It is true, the functions of the ganglia 
on the posterior roots, other than those just indicated, are un- 
known; on the other hand, the cells of the anterior horn are 
_ distinctly motor in function. To assume, then, that the cells 
of the ganglion are exclusively trophic, with the evidence now 
before us, would be premature. 
The view we have presented of the relation of the nervous 
system makes all cells trophic in a certain sense; and we think 
the view that certain cells or certain fibers are exclusively tro- 
phic must, as yet, be regarded as an open question. 
It is important, however, to recognize that certain connec- 
