600 PHYSIOLOGY. 



Cell-prolongations. From the researches of Deiters it has been 

 learned that nearly every nerve-cell has protruding from its periphery 

 a greater or less number of prolongations. These are of two vari- 

 eties: one is unique, nonbranching, and prolonged under the form 

 of a cylinder-axis of a nerve. It is known by the various terms, axis- 

 cylinder ', neuraxon, Betters' process, and neurite. The other variety of 

 prolongations is composed of many, though an uncertain, number of 

 processes. This new set of prolongations bears the name of proto- 

 plasmic processes., dendrons, dendrites, or the poles of the cells. Some 

 cells possess no dendrons, others very many. However, it is believed 

 that no cell is without its neuraxon. According to Cajal, the com- 

 munication of the prolongations of the cells among themselves is 

 no more than that of simple contact. It is analogous to the contact 

 which permits of the passage of the electrical current when the two 

 electrodes of an electrical battery are in contact. Further, the nervous 

 impulses are transmitted only along the neuraxons from cell to cell. 

 This neuraxon, by branching and coming in contact with the dendrons 

 of other and neighboring cells, conveys its impulse to them. They in 

 turn transmit it centripetally to the axis-cylinders of their own cells to 

 be further transmitted to other cells. The nerve-cell, according to 

 this doctrine, would be physiologically unipolar. To denote this close 

 contact existing between the axis-cylinder and dendrons of various 

 cells, Foster has used the term "synapsis." 



Bethe's Theory of Nerve-cell Connections. According to Bethe, 

 when a nerve is cut the nuclei of the neurilemma can regenerate a 

 new "band-fiber" without union with the central stump. Hence we 

 believe that the axis-cylinder is only an outgrowth from the nerve-cell. 

 According to Bethe, the neuro-fibrils go through the nerve-cells and 

 by a network are placed in direct communication with the neuro- 

 fibrils of other neurons. Here the cell has no direct activity in the 

 conduction of impulses from one part of the nervous system to the 

 other. The neuro-fibrils alone, and the cellular network within and 

 around the nerve-cells with which they connect, form the conduct- 

 ing track that at all points is in continuity. 



The nerve-cells of the gray matter are of various sizes and 

 shapes, the branched, stellate, or multipolar form being predominant. 

 Some are more or less bipolar or spindle-shaped; however, at each 

 extremity there is usually a fine plexus of branches. Some are ovoid 

 or pyriform, as in the cortex of the cerebellum, where they have 

 received the name of cells of Purkinje. The cells of the ganglia 

 of the spinal nerves are, in great part, unipolar. 



