44O THE CENTRAL NERVOUS SYSTEM. 



recognized a median ventral unpaired line of anastomosis and along 

 each half of the spinal cord four other lines of anastomosis. From the 

 median unpaired line of anastomosis some 200 to 2 50 branches pass 

 into the anterior fissure, each of which generally divides into a right 

 and left branch just in front of the commissure, each branch being 

 distributed to the gray matter in its immediate vicinity. The white 

 matter receives its blood-supply from vessels of the plexus in the 

 pia mater, from which numerous fine branches are given off which 

 terminate in capillary networks and extend as far as the gray matter. 

 The veins return the blood to the veins of the pia mater, following 

 in the main the course of the arteries. The central and peripheral 

 arteries do not anastomose except through capillaries and now and 

 then precapillaries (Adamkiewicz and Kadyi). 



In the cerebral cortex the capillaries are particularly numerous, 

 and are closely meshed wherever groups of ganglion cells occur. 

 In the medullary substance they are somewhat less closely arranged, 

 their meshes being oblong. In the cerebellum the arrangement is 

 analogous. Of all the layers composing the cerebellum the granu- 

 lar is the most vascular ; within it the capillaries are also densely 

 arranged and form a close network. 



Lymphatic vessels with definitive walls have thus far not been 

 discovered in the central nervous system. The blood-vessels through 

 the central nervous system are, however, surrounded by perivascular 

 spaces, which may be regarded as performing the function of lymph- 

 atic vessels. 



TECHNIC. 



The organs of the central nervous system are best fixed in Miiller's 

 fluid, washed with water, cut in celloidin, and stained with carmin. Such 

 preparations are suitable for general topographic work. 



Special structures as, for instance, the medullary sheaths of the nerve- 

 fibers, the ganglion cells, the relations of the different neurones and den- 

 drites to one another, etc. require different treatment. 



The medullary sheath may be demonstrated as follows (Weigert): 

 Pieces of tissue (spinal cord, for instance), fixed as usual in Miiller's or 

 Erlicki's fluid, arq transferred without washing to alcohol, imbedded 

 in celloidin, and cut. Before staining the sections it is necessary to 

 subject them to the mordant action of a neutral copper acetate 

 solution (a saturated solution of the salt diluted with an equal volume 

 of water). The sections may be subjected to the mordant action of 

 this solution, but the following procedure is more convenient : The 

 specimens, imbedded in celloidin and fastened to a cork or a block 

 of wood, are placed for one or two days in the copper solution just 

 described. At the expiration of this time the pieces of tissue will have 

 become dark, and the surrounding celloidin light green. They are then 

 placed in 80% alcohol, in which they may be preserved for any length 

 of time. The sections are then stained in the following solution : i gm. 

 of hematoxylin is dissolved in 10 c.c. absolute alcohol, and 90 c.c. of 

 distilled water are then added (the fluid must remain exposed to the air 

 for a few days) ; the addition of an alkali as, for instance, a cold satu- 



