NERVE-CELLS 219 



for the funiculi, the fibers running, for the most part, circularly. 

 The endoneurium not infrequently divides the nerve -bundles into 

 smaller or primitive bundles. It supports the blood -capillaries, 

 contains small lymph -spaces, and its nuclei are frequently large 

 and prominent. The larger nerve -trunks have their own nerves 

 distributed to the epineurium, nervi nervorum. 



The final distribution of the elements of a nerve -trunk is 

 effected by subdivision, first, of the large, and afterward of the 

 primitive bundles or funiculi. The perineurial sheaths are pro- 

 longed, surrounding the dividing bundles, even to their final distri- 

 bution, where, around terminal and single medullated fibers, the 

 sheath remains as a layer of exceedingly delicate flattened cells. 

 The necessity for the endoneurium ceases with the ultimate sub- 

 division of the funiculus. 



. The medullated nerve -fibers, when they reach the point of 

 their final distribution, branch at a node of Ranvier, and also lose 

 the medullary sheath. 



PRACTICAL DEMONSTRATION 



Medullated nerve-fibers can be studied best in preparations that have 

 been teased on a slide. It requires much care and patience to separate tho 

 single nerve-fibers of a bundle. The student should use nerve-tissue that 

 was fixed with osmic acid while fresh (see page 23). The medullary sheaths 

 are black. Also, tease nerve-fibers that were hardened in Muller's fluid and 

 afterwards washed and transferred to alcohol. Stain the fibers on the slide 

 with Van Gieson's picric acid and acid fuchsin mixture (page 32), omitting 

 the heematoxylin. Dehydrate with a few drops of alcohol in succession, 

 which may be removed with blotting-paper ; clear with a drop of oil of 

 cloves ; mount in balsam. The axis-cylinders and nuclei are red ; the med- 

 ullary sheaths are yellow ; the nodes of Ranvier are distinctly visible. 



A nerve that has been hardened in Miiller's fluid should be imbedded 

 in celloidin, and transverse sections cut ; stain with ha3matoxylin and Van 

 Gieson's picric acid and acid fuchsin. 



NERVE-CELLS 



The cells of the nerve -centers are usually called ganglion -cells. 

 They differ greatly in size, some of the largest measuring 100 p* or 

 more in diameter. The nucleus is round, conspicuous, and has a 

 nucleolus. The protoplasm sometimes contains pigment. The 

 cells are surrounded by minute lymph -spaces. Ganglion -cells 

 exhibit various shapes, some being spherical, others pyriform or 

 stellate. The differences in outline are due, in part, to the pro- 



