As far as I am concerned, the most important proof in favor of the neurone theory is not to be found in the histological appearanees, which are often very difficult to realize, but in the facts of embryology of the nervous system and in the phenomena of secondary degenerations, which are always limited to the area of the neuron, no matter whether one attacks the cell or the dependent fiber. If the ganglion cells are not nervous structures, what are they there for? They are extremely unsuitably placed if they serve for the nutrition of the fibrilla. And why should fibrilla not be nourished by the directly neighboring blood and lymph vessels, like all other body elements? But if the ganglion cell plays a leading part in the central nerve activity (as Hodge and others have shown by the appearance of its exhaustion following this activity), one can easily understand why the surrounding tissue (gray substance) is so vascular, while the fibers, which have only to conduct, are poorer in vessels.

The neurone theory thus presumes that the central nervous system is made up of a number of larger cell-fiber systems, inside which each cell-fiber element is, relatively speaking, equal to its neighbor. The cell-fiber element stands in contiguous connection (not in continuity) with its neighbor through side branches of the axis cylinder processes. They connect distant portions of the gray substance by means of fibrilla bundles of nerve processes, which are relatively isolated from one another, and which we call medullary fibers, in such a way that the end of the medullary fiber terminates in a treelike branching on the surface of the nerve cell. Besides, there are nerve cells of a second category (of Golgi), which have nerve processes, which spend themselves in branching in the immediate neighborhood of the cell (and in the same gray substance as the cell itself) without forming one or more medullary fibers. And, lastly, there are muscle neurons the terminal branchings of which are distributed in the muscles. The neurone theory, therefore, presumes that the ganglion cells are fibrillogenous, and not the neuroglia cells. According to this theory, the fib-rillum is a differentiation of protoplasm of the ganglion cell, having a specific nerve function.

According to the neurone theory, the activity of the nervous system consists of the following: Certain stimuli of a group of nerve elements are conducted along the long polypoid processes of the ganglion cells to other groups of like elements by means of simple contiguity1 1 of the molecular waves of stimulation, the neurokymes. We know that powerful increasing of stimuli (dynamogenesis), and just as powerful inhibiting of stimuli, take place within the central nervous system; but we do not know for certain which elements or portions of elements act inhibitorily, and which increase stimulation. Under certain circumstances it need not be separate elements or portions of elements, but it may depend on whether the stimulus waves accumulate or whether they neutralize each other by acting in opposing directions.

One can thus understand how the relatively equal valued groups of elements of the various areas of the cerebral cortex, together with their numberless polyp threads of the white substance, form a group of complex fibers - that is, of axis cylinders or fibrilla bundles - superordinated to the other centers. The concentrated activities of this group complex brings about the actual reflection of our superconsciousness. The stimuli of the special senses are projected in the cerebral cortex through the intermediation of the lower centers, and movement impulses coordinate by the system of the pyramidal cell fibers 3 are conducted from this cortex, as are the inhibitions of reflex of the reflex centers in the medulla oblongata, in the spinal cord, etc. The most complicated combinations of increase of stimulation, of conduction, and of inhibition within the whole central nervous system and between the centers and periphery - both centrifugally (motor) and centripetally - come into play in every menial activity, and in all alternating actions of perception and of our dealings. In this the conduction is carried out by the fibrilla bundles encompassed by medullary sheaths, which we call axis cylinders or nerve fibers, and which are isolated for long stretches. A further isolation takes place

1 The contiguity might bo transformed into continuity under certain circumstances, us the result of secondary adhesions.

2 By this I mean large crossed bundles of tillers which belong to the neurons of the largest ganglion cells of the cortex (the so-called central convolutions), and which connect these cells directly with the large motor ganglion cells of the anterior horns of the spinal cord, etc. The last named form the muscle within the same through the fibrilla, which can conduct, being completely isolated in themselves after their branching or "unbinding" (somewhat like the individual wires of a transatlantic telegraph cable).

But we must remember that many element systems of coordinated and superordinated centers are always simultaneously active, and carry over to one another their waves of stimulation.

We must, further, not forget that all our subjective sensations, that is, those of which we are conscious - there are no objective sensations: this would be a contradictio in adjecto - take place in the cerebrum; and the same applies to all the complex collections of sensations which we call perceptions, no matter by what sort of stimulation or combination of stimuli they are effected. All activities of the nervous system leave a trace behind them after they have taken place, or show a changed molecular arrangement of the whole coordinated complex, which one can call engram or impression of memory. Many parts of such engrams undoubtedly oscillate (or lie) in every nerve element. These traces possess, as is well known, the peculiarity that they can be ecphorized after a long time by means of an associated stimulus - i.e., that they can be transformed into an activity which is almost identical with the first stimulus, even if it is mostly less powerful. We call the subjective reflection (in the consciousness) conception.