I 



AREANGEMENT OF THE NERVOUS SYSTEM 567 



become connected with their cell-bodies. It has also been proved by 

 this investigator that the cell-body is not essential to conduction. 

 This has been demonstrated in Carcinus msenas in which the nerve 

 of the second antenna is composed of centrifugal and centripetal 

 fibers and connects with a ganglion the cell-bodies of which are situated 

 somewhat apart from the fiber network or neuropil. On removing 

 the former, it was found that the antenna regained its former tonus 

 very rapidly and that its stimulation gave rise to reflex actions. Ob- 

 viously, in this case conduction is had even in the absence of the 

 cell-bodies by means of the fibrillar network or neuropil. Steinach^ 

 has shown that this condition may be duplicated by causing the cell- 

 bodies of the dorsal root ganglion to degenerate or by removing this 

 ganglion in its entirety. Curiously enough, the sensory impulses 

 continue to pour into the spinal cord even in the absence of this gan- 

 glion, and hence, it may be inferred that they reach the central end of 

 the posterior root without being required to make station at this point. 



Arguments in Favor of the Neuron Doctrine. — Regarded in a very 

 general way, it may be said that nervous processes are of two kinds: 

 namely, generative or central and conductile or peripheral. The 

 former include the automatic production of impulses and psychic 

 activities such as volition, thought, perception, and others. The 

 latter, on the other hand, merely represent the phenomena of conduc- 

 tion accompanying the passage of an impulse through an axon. In 

 perfect harmony with this functional division, the nervous system 

 presents itself as gray matter and white matter; the former constituting 

 the central nuclei and centers of function, and the latter the paths of 

 conduction by means of which these complexes of ganglion cells are con- 

 nected either with one another or with peripheral effectors and recep- 

 tors. Physiologically, it is quite impossible to attribute the genera- 

 tion of impulses to the conducting element of the neuron, the fibrillse. 

 In other words, creative processes can only be referred to the constitu- 

 ents of the gray matter, the cell-bodies. Thus, the different phenom- 

 ena of consciousness, the automatic activity of the centers, and other 

 processes, can only be produced by the cellular units of the gray matter 

 and not by the fibers alone, and hence, the liberation of nervous 

 energy is distinctly a duty of the cells. 



A similar conclusion must be drawn from the time relationship 

 between impulses traversing nerve fibers and impulses passing through 

 nuclei and centers. It is a well-established fact that their journey 

 through nerve fibers requires a much shorter time than their passage 

 through centers. The deduction to be derived from this is that the 

 ganglion cells possess a specific activity which directly affects the 

 nature of the impulse. 



Looked at from the standpoint of embryology, the fibrillar concept 

 fails to establish a structural unit, because the axis cylinders of the 

 nerve fibers do not arise from outgrowths of the cell-bodies, but from 



1 Pfliiger's Archiv, cxxv, 1908, 239. 



