SPINAL CORD. 99 



obtained. The process of teasing is best accomplished with the aid of a dissecting microscope, 

 but the preparation ought to be examined from time to time with a low power. A hair or 

 thin piece of paper ought to be placed under the cover-glass, to prevent the cells from being 

 displaced. 



(If) Injection of Osmic Acid. By means of a subcutaneous syringe, provided with a very fine 

 gold nozzle, inject forcibly a small quantity of a half per cent, solution of osmic acid into the 

 anterior horn of a perfectly fresh spinal cord. This serves to separate the parts, and at the 

 same time to fix them. Macerate the part for two days in dilute alcohol, and isolate the cells 

 by carefully teasing out a piece, as described under (). 



(c] Dilute Osmic Acid. Macerate pieces, the size of half a pea, of the grey matter of the 

 anterior horn of a perfectly fresh cord in a considerable quantity of a tenth per cent, solution 

 of osmic acid for ten days. Wash away the greyish deposit, and place the pieces in a mixture 

 consisting of equal parts of glycerine and water, for ten days or a fortnight. Tease a small 

 piece in glycerine. The cells are easily stained with a very dilute solution of magenta. 



EXAMINATION (L and H). Observe the large multipolar cells, with many branched 

 processes. One process the axis-cylinder process, which is directly continuous with the 

 axis-cylinder of a nerve-fibre is always unbranched. Observe the large nucleus, and note the 

 longitudinal striation of the cell-substance and that of the axis-cylinder process. 



BLOOD-VESSELS OF THE SPINAL CORD. 



An entire animal must be injected, and sections made of the injected cord. The grey 

 matter is much more vascular than the white. The sections are mounted in dammar, and 

 need not be stained. 



The connective tissue of the subarachnoid space has already been referrd-te-(p. 23). 



/tC^ E U BK - ' \ 

 /, > 



THE MEDULLA 



PREPARATION. The same methods as are employed for the spinal cord are-terbe used. 

 Make transverse sections of the human medulla, some through the decussation of the anterior 

 pyramids, and others through the floor of the medulla and the olivary bodies. Stain them 

 with aniline blue-black, and mount in dammar. 



EXAMINATION (L). Transverse Section through the decussation of the Pyramids. Observe 

 the crossing of the fibres from one side to the other ; notice the enlarged posterior cornua 

 (tubercles of Rolando), the central canal nearer the surface posteriorly. 



Through the Olivary Body. Observe the median raphe ; the central canal has now ex- 

 panded into the floor of the fourth ventricle. Study the columns of the medulla from the 

 centre in front outwards as anterior pyramids, olivary body, restiform body, and posterior 

 pyramid on each side. Notice the folded sheet of grey matter corpus dentatum in the 

 olivary body, and in it notice the multipolar nerve-cells. Observe the masses of grey matter 

 in the floor of the fourth ventricle. 



o 2 



