THE BRAIN AND SPINAL CORD. 245 



across the laminae, for example) are made, as thin as 

 possible under the circumstances one-tenth of an 

 inch thick perhaps and are placed in a strong 

 watery solution (seven per cent.) of the aniline-blue- 

 black. After three hours the staining solution is 

 poured off and water substituted, and in a few 

 minutes this, which will still be intensely colored, 

 is replaced by fresh water, and so on until the excess 

 of the staining fluid is washed away from the slices. 

 If one is cut in half it will be seen that only the sur- 

 faces are stained, the aniline solution not having 

 penetrated to the interior. When the washing is 

 completed the slices are transferred from the water 

 to glass slides. This can be effected, without risk 

 of breaking the sections, by floating them on to an 

 immersed slide, and raising both together out of the 

 water. The excess of water is then allowed to drain 

 off', and the pieces are left in a dry place exposed to 

 the air, so that after twenty-four or at most forty- 

 eight hours, they will be found firmly dried to the 

 glass. In the process of dry ins; they will have lost 

 a good deal in thickness, and this is now still further 

 reduced by planing off the upper stained surface with 

 a razor, or other suitable instrument, without scrap- 

 ing away at any place, if it can be helped, the lower 

 stained part which is adherent to the slide. The 

 further preparation consists in covering the section 

 w r ith a thin layer of dammar varnish (oil of cloves 

 is not requisite); after which it may be examined 

 with the microscope, and, if it appears satisfactory, 

 a cover- glass added. 



There is hardly any limit to the size of which a 

 section of the brain may be obtained by this method, 

 and, if due care be taken with the planing down of 

 the section, it is in nearly every case attended with 

 success. In addition to exhibiting nerve-cells, the 

 method is useful for following the course of tracts 

 of nerve-fibres in the nervous centres, since, owing 

 to the depth of staining of the axis-cylinders, the 

 nerves may be traced for considerable distances. 



21* 



