96 PRACTICAL HISTOLOGY. 



extremely small piece must be taken. Place it on a slide, 

 add no fluid, gently press down the cover-glass, and examine 

 the fibres. As the white fibres in the brain and spinal cord 

 are not surrounded by a gray sheath, they readily yield to 

 .the influence of pressure, becoming ampullated, and even 

 broken into pieces. The fragments assume a rounded 

 form, each one being marked like the original fibre by a 

 double contour. This serves to distinguish them from nerve 

 cells, for which they are apt to be mistaken by the inex- 

 perienced observer. 



152. T. S. sciatic nerve of rabbit or cat hardened in 

 chromic acid ( 14). Stain with logwood ( 323) by placing 

 the section in a large drop of logwood solution on a slide. 

 After staining and washing in water, remove the water 

 by immersing first in methylated spirit in a watch glass, 

 and then in absolute alcohol for two or three minutes. 

 Lay the section on a slide, allow it to partially dry (let it 

 just become glazed and sodden), then insinuate a drop of 

 clove oil under the section with a sable-hair brush (camel- 

 hair is not stiff enough). Allow the oil to rise through the 

 section, and so drive away the spirit. The principle of 

 this method is explained in 3 47 A. 



(L.) Watch the clarifying effect of the oil (the section 

 being still uncovered, of course). Finish the clarification 

 by touching the upper surface of the section with the oil. 

 Lastly, cover with a drop of dammar or Canada balsam 

 solution, put on the cover-glass, and gently press it down. 

 Water and spirit are not miscible with dammar. The spirit 

 replaces the water, the clove oil replaces the spirit, increases 

 the transparency of the tissue, and is miscible with dammar 

 or Canada balsam dissolved in benzole or chloroform. 



(H.) In the section prepared and mounted as above, 

 divided nerve fibres of various sizes are seen, each with 

 a violet centre the axial cylinder surrounded by the 

 medullary substance unstained. Observe the connective 

 tissue (neurilemma, perineuriuni) forming a sheath to the 

 nerve, and sending processes between the fasciculi of the 

 nerve fibres. 



153- Gray nerve fibres. (H.) Examine a preparation 



