ORIGINAL COMMUNICATIONS. 



Observations on the Structure of Nerve-Fibre. 

 By J. Lockhart Clark, Esq., F.R.S. 



Whenever we wish to ascertain the natural appearance 

 and structure of the nerve-cells and nerve-fibres, these tissues 

 should be examined in some transparent part during life, or 

 on removal immediately after death, and with the addition 

 only of a little serum of the blood. But when it is intended 

 to investigate, in the nervous centres of the vertebrata, the 

 mutual relation of these elementary parts, and their natural 

 arrangement, such as the grouping of the cells and the course 

 of the fibres, it becomes necessary to harden the nerve- 

 substance in some kind of fluid, so that it may be cut into 

 thin sections, which can then be rendered more transparent 

 by a further process. The method which I extensively em- 

 ploy for such investigations is as follows : 



The part intended for examination should be as fresh as 

 possible, and cut into pieces as small as compatible with the 

 particular end in view. These pieces I formerly hardened 

 by means of a mixture of one part of spirit of wine and three 

 parts of water, which, at the end of twenty-four hours, Avas 

 replaced by a fresh mixture of equal parts of spirit and water, 

 and this again, after the same interval, by pure spirit, which 

 ought to be renewed every five or six days. But for the last 

 three years 1 have used chromic acid instead of spirit, 

 in the process of hardening. The spinal cord of man, of 

 the Ox, Sheep, and other large vertebrata, is steeped in a so- 

 lution of one part of crystallized chromic acid in two hundred 

 parts of water, for two or three weeks, and then placed in a 

 solution of one part of bichromate of potash in one or two 

 hundred parts of water. For the hemispheres and the 



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