130 PRACTICAL HISTOLOGY. 



a piece of the spinal cord from the lumbar region 

 may be taken, for the nerve-cells are here very 

 numerous and consequently more readily found 

 than in other regions. 



Preparation 5, The human spinal cord is, if 

 obtainable, best adapted for the study of the cells, 

 for they are readily picked out under the dissecting 

 microscope, in consequence of the little mass of dark 

 pigment which each contains. If a piece of the 

 human spinal cord cannot be got, the spinal marrow 

 of the ox or sheep, or other tolerably large animal, 

 may be employed. The piece to be macerated 

 should be about half an inch long, and is placed for 

 forty-eight hours in weak bichromate of potash 

 solution (1 in 800). At the expiration of this time 

 it is taken out of the fluid, and with the point of a 

 scalpel or of fine scissors a small piece of the gray 

 matter is dug out from the anterior cornu, placed in 

 a drop of water upon a slide, and separated with 

 needles into three or four pieces. These are then 

 placed under the dissecting microscope and carefully 

 broken up further ; those parts where the cells are 

 most numerous being singled out, and the prepara- 

 tion being examined every now and then on the 

 ordinary microscope with a low power, in order that 

 the progress of the isolation may be watched. When 

 as much as possible has been effected in the way of 

 separating the nerve-cells a piece of hair is placed 

 in the fluid and the cover-glass gently superposed. 

 The cells may then be sought with a low power and 

 carefully examined with a higher one. 



If the preparation is very successful, and it be 

 desired to preserve it, keeping the cells at the same 

 time as much as possible of their natural aspect, the 

 best plan to adopt is to allow a drop or two of a 1 

 per cent, solution of osrnic acid to flow in at the edge 

 of the cover-glass, and after it has acted upon the 

 tissue for an hour, by which time the cells will have 

 'become stained of a dark grayish tint, to carefully 

 run through from the same side first a little distilled 



