XXX.] SPINAL CORD. 339 



desired to show. Two hours or so are enough for the cord, but 

 if the fine plexuses of medullated fibres described by Exner in 

 the cerebral cortex are to be well seen, let them stain for twenty- 

 four hours. After they are sufficiently stained, throw the watch- 

 glass and the stained sections into a large basin of distilled water. 

 Remove the sections from the water at once, and place them, for 

 about half an hour or more, in the following mixture : 



Potassic ferricyanide . . . 2.5 grams. 



Borax . . . . . 2 ,, 



Water ..... 100 cc. 



This fluid decolorises and differentiates the black sections. The 

 grey matter becomes of a brown or light-yellow tint, and should 

 remain so while the white matter becomes violet. The sections 

 must remain in the decolorising fluid until the deep blue or violet- 

 coloured medullated nerve-fibres are seen. This can readily be 

 determined after a little practice. The sections are then washed 

 in water in which they can be kept for a considerable time 

 transferred to 90 per cent., and finally to absolute alcohol, clari- 

 fied by xylol or origanum oil, and mounted in xylol-balsam. This 

 method stains the medulla or myelin of the nerves especially of 

 the central nervous system of a deep blue or violet tint, while the 

 nerve-cells, neuroglia, and axis-cylinders are not stained. The 

 method, however, may be combined with staining methods. After 

 the organ is hardened in the chromium salt and alcohol, small pieces 

 are embedded in celloidin and cut in a microtome. The sections 

 are placed in 80 per cent, spirit not water. The celloidin enables 

 the sections to be readily handled and transferred to a slide. They 

 are then stained in the special haematoxylin fluid already described. 

 If a series of sections is to be mounted on the same slide, see the 

 method described at p. 60. The sections are clarified in origanum 

 oil or a mixture of xylol and carbolic acid (p. 83). Mounted in 

 balsam. This method is also applicable to the spinal ganglia. 



(B.) Freezing Method. The piece of cord or brain, after harden- 

 ing in M tiller's fluid, is placed in spirit and transferred to a mixture 

 of equal parts of absolute alcohol and ether, and then embedded in 

 celloidin. The embedded tissue is placed for forty-eight hours in 

 Erlicki's fluid, to get rid of the spirit, and they are then placed in 

 the following mixture, and kept in stoppered bottles in a warm 

 chamber at 38 C. for two or three days : 



Cupric sulphate . .... 0.5 gram. 



Potassic bichromate .... 2.5 grams. 

 Mucilage of syrup and gum . . . 100 cc. 



Sections are cut in a freezing microtome and received into Krlicki's 

 fluid, washed in methylated spirit, stained in the hamiatoxyliii fluid, 



