STRUCTURE OF THE GREY SUBSTANCE OF THE SPINAL CORD. 345 



to lose their sharpness of outline if the solution of gold has 

 been too strong, or if they have lain too long in it. 



The second method, which consists in a peculiar application 

 of carmine and ammonia, has this advantage over the one above 

 described, that the relations of the plexus of nerve fibres to the 

 nerve cells, which are not clearly brought into view by the 

 treatment of chloride of gold and potassium, are distinctly 

 exhibited. For this purpose, perfectly fresh and still warm 

 segments of the spinal cord are requisite, and may best be 

 obtained from the Calf or Ox. Longitudinal sections, especially 

 through the anterior nerves, and as fine as possible, are made 

 from these with a razor ;* these are immediately placed in an 

 extremely weak solution of bichromate of ammonia (containing 

 one part in 5,000 to 10,000 parts of water), and allowed to re- 

 main for two or three days in a cool temperature. They are then 

 immersed in a very dilute solution of carmine and ammonia, 

 in which they acquire, in the course of twenty-four hours, the 

 depth of colour requisite for further preparation. And now, 

 after being thoroughly washed with distilled water, the thinnest 

 parts of the sections, which are at the same time the most 

 deeply stained, are broken up with needles under a lens, when 

 the nerve cells, which appear as darkened spots, together with 

 the adjoining portions of the plexus of nerve fibres, may be 

 readily isolated. The preparations may either be preserved in 

 glycerine, or, which is still better, the water may be allowed 

 to evaporate, and the dry object, after the addition of a 

 small quantity of oil of cloves, may be put up in Canada 

 balsam. 



The importance of both methods for the examination of the 

 grey substance of the spinal cord is very great, because they 

 enable the fibres of the neuroglia, which are of equal tenuity, 

 but are not stained either by the chloride of potassium and 

 gold or by carmine and ammonia, to be distinguished from the 

 true nerve fibres. Large fibres spring from the plexus of nerve 

 fibres, that either coalesce to form still larger ones (fig. 223), 

 and traversing the grey substance reach the white columns 



* The fresher the spinal cord, the more easily are very fine sections 

 made, as the consistence of the cord diminishes rapidly after death. 



