72 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



cylinder breaks up into its elementary fibrillae, to end in various ways to 

 be described later. 



THE NERVE -CELL BODY. 



The nerve-cell body is the nodal and important part of the neurone, and 

 from it are given off the dendrites and axis-cylinder process or axone. It 

 consists of a mass of protoplasm, of varying shape and size, containing within 

 it a nucleus and nucleolus. All nerve cells give off one or more processes 

 which branch out in various directions, dividing and subdividing like the 

 branches of a tree, but never anastomosing with each other or with other cells. 



FIG. 95. Ganglion Cells, Showing Neurofibrils. A, Anterior-horn cells of human; B, cell 

 from the facial nucleus of rabbit; C, dendrite of anterior horn cell of human. (Bethe.) 



These branches are what have already been referred to as the dendrites of 

 the cell. They were formerly called the protoplasmic processes, figures 91, 

 93. It is thus seen that the neurone or nerve unit consists of a number of 

 subdivisions, namely, the cell body, with its nucleus and nucleolus, the 

 dendrites or protoplasm processes, and the axone or axis-cylinder process. 



The protoplasm of the cells is shown by various dyes to consist of neuro- 

 fibrils, perifibrillar substance) and in most cells chromophilic bodies. Apathy 

 and others have demonstrated that a network of interlacing and anasto- 

 mosing fibrils traverses both the cell body and its branches, figure 95. 



The perifibrillar substance is a fluid or semifluid substance in which the 

 fibrils are embedded. By treating nerve cells with special stains granular 

 bodies varying in size are found embedded in the cytoplasm. These bodies 

 are the chromophilic bodies, figure 96. 



