CENTERS IN THE SPINAL CORD 585 



lus is delayed by passing through the ganglion i. e., whether a reflex response 

 evoked by stimulation of an afferent nerve will take place any earlier when the 

 stimulus is applied central to the ganglion than when applied peripheral thereto. 

 Wundt, in fact, found a delay in the reflexes from the spinal ganglion of a frog 

 amounting to 0.003 second. Neither Exner nor Moore and Reynolds, however, 

 were able to demonstrate such a delay. Gad and Joseph studied the jugular gan- 

 glion of the vagus, which is the homologue of the spinal ganglia, and used as 

 an indicator the change in respiratory movements produced by stimulation. It 

 was shown that as a mean result of a large number of readings the reaction 

 appeared 0.036 second earlier when the stimulus was applied central to the gan- 

 glion than when applied peripheral to it. If these observations are confirmed 

 we shall have proof that in this ganglion, at least, 

 every impulse traversing a fiber afferent to the gan- 

 glion passes through a nerve cell. 



But it appears to be unnecessary that the im- 

 pulse should pass through the body of the ganglion 

 cell. In the crab, Carcinus mwnas, Bethe observed 

 that the tonus of the muscles moving the antennae 

 persisted and reflex contractions could be induced 

 in them after the mantle of solid ganglion cells 

 inclusive of their nuclei had been pared off the 

 cerebral ganglion which controls these muscles. 

 In this case the excitation had been propagated 

 through the fibrillary reticulum (cf. page 560) FlG - 26a 



still connected with the nerve fibers. Here we have / 



indubitable evidence of the importance of nerve fibrils as conducting elements 

 in the nervous system. It is true that the phenomenon could only be observed 

 for some two or three days after the operation ; but this was to be expected, since 

 we know that nonnucleated cell fragments cannot live indefinitely. 



Similar phenomena have been observed in the spinal ganglia of the verte- 

 brates. Langendorff was able to show among other things that the posterior 

 roots in the frog give an action current when stimulated peripherally to the 

 ganglion, as much as twenty-four hours after the heart had been extirpated 

 i. e., at a time when reflex movements had long since ceased. Shortly after this 

 Steinach demonstrated for the same animal that ganglia which had lain for 

 forty-eight hours in physiological salt solution were still permeable to the action 

 current. The same thing took place if a ganglion in the living animal were 

 deprived of its blood supply for fourteen days. In both cases, to judge by micro- 

 scopical appearances, all the ganglion cells had degenerated. 



From all this it ought to be regarded as at least probable that an impulse 

 can be propagated through an afferent spinal nerve without traversing the cell 

 body of the corresponding ganglion cell. 



9. CENTERS IN THE SPINAL CORD 



The spinal cord has a twofold function : it acts as an independent central 

 organ, and serves as a great highway to connect the tributary afferent and 

 efferent pathways with the brain. 



35 



