EXAMINATION OF THE NBKVOUS SYSTEM. 



653 



Fig. 346. 



EXAMINATION OF THE NERVOUS SYSTEM. 



Brain. — As the nerve-fibres rapidly undergo change, the brain 

 should be examined very soon after death, by depositing minute 

 portions upon a perfectly clean 

 slip of glass, and moistening 

 them with serum or a weak sac- 

 charine solution. If it is desired 

 to examine the distribution and 

 arrangement of nerve-fibres, the 

 brain should be placed in a solu- 

 tion of chromic acid; by the 

 hardening thus produced it can 

 be easily cut into thin slices by 

 means of a Valentin's knife. 

 The addition of water to a por- 

 tion of white cerebral matter 

 changes the natural appearance 

 of these fibres, by separating the 

 oily and albuminous contents of C 

 the tubular sheath. The oily 

 matter collects into globules, 

 giving a beaded appearance to 

 the fibres. (Fig. 346, ^, ^'.) The 

 nerve-tubes may be rendered very 

 distinct by the addition of a dilute 

 solution of caustic soda. • 



Small portions of the meninges 

 of the brain may be examined in 

 the same manner. 



To examine the cerebral vessels, a thin section must be well 

 washed, and subjected to gentle pressure. The vessels are thus 

 deprived of their investing neurine, and may now be rendered 

 more distinct by the dilute caustic soda. 



The corpora amylacea, or gritty particles found in the pineal 

 gland and other parts of the brain (Fig. 347), must be separated 

 from the nervous tissue for examination by repeated washing 

 in water. 



Spinal Cord. — To examine the spinal cord with advantage, it 

 should first be hardened in a solution of chromic acid, or in 

 spirits of wine. The structure of thin sections is thus rendered 

 quite conspicuous. The following method was employed by Mr. 

 J". S. Clarke.i 



"A perfectly fresh cord was hardened in spirits of wine, so 

 that extremely thin sections, in various directions, could be made 

 by means of a very sharp knife. A section so made was placed 

 on a glass slide, and treated with a mixture composed of one part 

 of acetic acid and three of spirits of wine, which not only makes 

 the nerves and fibrous portion more distinct and conspicuous, 



' Philosophical Transactions, 185], Part ii. 



