Nov. I. I9I9 Pathology of Dourine 147 



composed of a cell body, nucleolus, nucleus, chromatic substance, achro- 

 matic substance, pigment, and processes. It would also include the proto- 

 plasmic processes with their gemmules and the axis-cylinder process, its 

 collaterals, and at times a final arborization. The term chromatic or 

 chromatophil substance, or Nissel's bodies, is applied to that portion of the 

 cell substance which stains and has an affinity for methylene blue. It 

 presents itself in many forms as irregular particles, smooth or dented 

 fibers, or dumb-bell-shaped masses. The function of the chromatic sub- 

 stance has not up to the present time been definitely determined. The 

 achromatic substance constitutes the greater part of the cell body and is 

 made up of fine fibrils which pass through the cell with numerous anas- 

 tomoses which gives this substance a finely reticular appearance. Certain 

 observers consider the fibrils as the continuations of axones on their way 

 into the processes. According to this view the achromatic substance is 

 the all-important part of the cell. 



The nerve fibers, on the other hand, are not independent elements but 

 are those processes of the neuron known as the axon or axis-cylinder 

 processes, which after their exit from the cell body extend and become 

 invested in a protecting sheath. They are then known as the medullated 

 nerves. The essential part of the nerve fiber is the central cord or axis 

 cylinder, which is the only part concerned in transmitting the nerve im- 

 pulse. The axis cylinder is composed of most delicate axis fibrillae 

 embedded within a semifluid interfibrillar substance and is surrounded 

 by a delicate sheath, the axilemma. The axis cylinder is surrounded on 

 the periphery by a relatively thicker coat, the medullary sheath or white 

 substance of Schwann, outside of which lies the delicate enveloping coat, 

 the neurilemma. The medullary sheath is composed of a delicate retic- 

 ulum of neurokeratin, the meshes of which are filled with a fatty sub- 

 stance, the myelin. This constitutes the majority of the peripheral 

 medullated nerve fibers, but the medullated fibers of the spinal cord have 

 no neurilemma. 



The nerve fibers in the sympathetic system have no medullary sheath 

 and are spoken of as the nonmedullated or gray fibers. The nerve cells 

 and nerve fibers within the central nervous system are held together by 

 a special supporting tissue, the neuroglia, which consists of an interlacing 

 network of extremely fine fibrillae, the glia fibers, and glia cells. The 

 cells are irregularly scattered in the course of the glia fibers. 



Of the different fixing fluids, a 4 per cent solution of formaldehyde was 

 used as a preliminary fixative more often than any other on account of 

 its great power of penetration and rapid fixation. It must be followed, 

 however, by other reagents such as Miiller's fluid or Zenker's fluid, con- 

 taining chrome salts, which bring out more clearly the ganglion cells, 

 neuroglia, and axis cylinder. The chrome salt probably enters into 

 chemical combination with the myelin, thus making possible the use of 

 differential my el i n sheaths stain. 



