96 PRACTICAL HISTOLOGY. 



THE NERVOUS SYSTEM. 



THE SPINAL CORD. 



PREPARATION (a). Miiller's Fluid and Spirit Mixture. Remove the spinal cord and 

 medulla oblongata, with the pia mater attached, from a newly-killed cat, rabbit, or dog. 

 Indeed, all the membranes may be left attached to the cord. Take care to avoid squeezing 

 or stretching the cord. It is not necessary to make any incisions into the cord at 

 first. Suspend it in a wide, cylindrical vessel such vessels as are used for water analysis do 

 very well filled with a mixture composed of three parts of Miiller's fluid, and one of methylated 

 spirit. The mixture ought to be made at the time ; but as a considerable amount of heat is 

 evolved when the fluids are mixed, it ought to be allowed to cool. Keep the tissties in a cool 

 in fact, a cold place. This is of great importance. Renew the fluid at the end of twenty-four 

 hours, and then again at the end of a week. The cord may now be cut, with a sharp razor, into 

 segments an inch or so long. The cord ought to be hardened in this mixture for three weeks. 

 It is then transferred to a two per cent, solution of ammonium bichromate for two weeks, to 

 complete the hardening. Preserve them either in spirit, or in a solution of chloral hydrate, 

 of twelve grains to an ounce of water (Hamilton). A portion of the spinal cord of a man or 

 an ox ought to be hardened in the same way. 



(V) Potassic-bichromate. Cut the fresh spinal cord of an ox into pieces an inch long by 

 means of a sharp razor. Place them in a large quantity of two per cent, solution of potassic 

 bichromate. Do not let one piece lie on another. See that they are separated by cotton 

 wool, previously dipped in alcohol, to avoid pressure. It requires from three to five weeks to 

 complete the hardening. Preserve the cord in spirit. A cord hardened in this way shows the 

 nerve-structures very well. 



(c) Chromic Acid and Spirit Mixture. The cord must be cut into pieces half an inch long 

 and placed in this fluid, which will harden them in from two to three weeks. It is not so well 

 suited for showing the nerve-elements as for demonstrating the neurogleia. 



(d) Spirit and Iodine, and then Ammonium-bichromate. Suspend the cord in a long, cylindrical 

 vessel, in methylated spirit tinged yellow with tincture of iodine. Leave it in this mixture 

 usually three or four days until the yellow colour has nearly disappeared. Cut it in pieces 

 an inch long, and complete the hardening by keeping them in a two per cent, solution of am- 

 monium-bichromate for four or five weeks. Preserve them in spirit until required for section. 



METHOD OF CUTTING SECTIONS OF THE SPINAL CORD. 



Employ some form of freezing microtome. Steep a piece of the cord, hardened by any 

 of the above methods, but preferably by (a), in water for twenty-four hours, to remove 

 all traces of the hardening agent, or the spirit. Soak it in syrup (two ounces of sugar to 



