344 THE SPINAL CORD, BY J. GERLACH. 



plexus, which, together with the nerve cells, confer its peculiar 

 characters upon the grey substance. These plexuses are not 

 visible in the perfectly fresh spinal cord, and the application of 

 other reagents is required to render them apparent even in 

 spinal cords that have been treated with the salts of chromic 

 acid. As the plexuses of these nerve fibres of the grey sub- 

 stance are still but little known, it will be convenient to 

 describe shortly the mode of bringing them into view. 



When it is desired to treat fine sections of the spinal cord 

 with the double chloride of potassium and gold, some mode of 

 hardening the tissue must be previously adopted, and for this 

 purpose a 1 to 2 per cent, solution of double chromate of 

 ammonia is preferable to all other preparations of chromic 

 acid. Small portions of the perfectly fresh spinal cords of 

 infants, macerated for fifteen or twenty days in this fluid at 

 a low temperature, acquire a proper degree of hardness for 

 making the section. The plexuses are shown beautifully, in 

 proportion to the shortness of time required to harden them. 

 For the preparation of extremely fine sections, which however 

 do not include the whole diameter of the cord, I have employed 

 my improved form of Welker's microtome* 



The sections should be placed in a solution containing one 

 part of double chloride of potassium and gold in ten thousand 

 of water that has been feebly acidified with hydrochloric 

 acid, and in this they may be allowed to remain for ten or 

 twelve hours, till they have slowly acquired a pale lilac colour. 

 They should then be washed in a solution containing one part 

 of hydrochloric acid in from 2,000 to 3,000 parts of water, and 

 dipped for ten minutes in a mixture of 1,000 parts of a 60 per 

 cent, solution of alcohol and one part of hydrochloric acid, then 

 immersed for a few minutes in absolute alcohol, and finally 

 rendered transparent in oil of cloves, and put up in Canada 

 balsam. The plexus of nerves is even then not quite distinctly 

 visible at first, but becomes better defined in the course of 

 three or four hours, again blackening to so great an extent as 



* J. Gerlach, Zur Anatomic des menschlichen Ruckenmarks. " The 

 Anatomy of the Spinal Cord of Man." Med. Centralblatt Jahrg., 1867, 

 No. 24, 



