THE NERVOUS TISSUES. 149 



branches ; these are the dcndrites, dendrons, or protoplasmic branches. 

 In the spinal ganglia and the homologous cranial ganglia these mor- 

 phologic differences in the processes are not observed, the neuraxis 

 and the dendrites of each presenting essentially the same structure. 



To the entire nerve -cell, cell-body and processes the term 

 neurone (Waldeyer, 91) has been applied; ncnra (Rauber), or neu- 

 rodendron (Kolliker, 93). 



The neuraxes of many neurones attain great length. Those of 

 some of the neurones, the cell-bodies of which are situated in the 

 lower part of the spinal cord, extend to the foot. In other regions 

 neuraxes nearly as long are to be found, and in the majority of neu- 

 rones the neuraxes terminate some distance from the cell-body. It is 

 therefore manifestly impossible in the majority of cases to see a neu- 

 rone in its entirety. Usually, only a portion of one can be studied 

 in any one preparation. Consequently, the more detailed descrip- 

 tion which follows will deal with the neurone in this fragmentary 

 manner. The cell-bodies of the neurones, to which the term 

 "nerve-cells" or "ganglion cells" is usually restricted, the den- 

 drites and neuraxes, often forming parts of nerve-fibers, and their 

 mode of terminating, will receive separate consideration. 



NERVE-CELLS, OR GANGLION CELLS ; THE CELL-BODIES OF 



NEURONES. 



The cell-bodies of neurones are usually large. The bodies of 

 the motor neurones of the human spinal cord measure 75 to 150 //, 

 their nuclei 45 //, and their nucleoli 1 5 /u. The smallest nerve-cells, 

 the neurones of the granular layer of the cerebellum, are 4 to 9 fi in 

 diameter. The protoplasm of nerve-cells shows a distinct fibrillar 

 structure and the fibrils may be followed into the processes. (Fig. 

 107.) Their nuclei are also large, with very little chromatin, but as 

 a rule are supplied with a large nucleolus. 



After treatment by certain special methods, the protoplasm of 

 the ganglion cells shows granules or groups of granules which show 

 special affinity to certain stains, consequently known as chromato- 

 phile granules ; these are densely grouped around the nucleus, so 

 that the cell-body shows an inner darker and an outer lighter por- 

 tion. These chromatophile granules, also spoken of as tigroid 

 granules or as the tigroid substance (v. Lenhossek), as a rule are not 

 arranged in concentric layers, but lie mostly in groups, giving to the 

 protoplasm a mottled or reticular appearance. In the cells of the an- 

 terior horns (man, ox, rabbit) the granules join to form flakes, which are 

 also more numerous in the region of the nucleus. In all cases the 

 granules or flakes are continued into the dendrites of the cell. Here 

 they change their shape into long pointed rods, with here and there 

 nodules, which are probably the chief causes of the varicosities so 

 often seen in dendrites (Golgi's method). The cell usually has a 

 clear, nongranular peripheral border (not a membrane), and in the 



