66 ELEMENTS OF NERVOUS TISSUE. 



4 



number of processes, according to Leydig, as there are 

 nerves connected with the ganglion (PL XII. fig. 

 IV.). The study of the relations which exist between 

 nerve cells and nerve fibres is one of difficulty ; very 

 thin sections must be made of fresh specimens of 

 ganglia, and treated with dilute acetic acid, or caustic 

 potassa, or still better, perhaps, by a solution of car- 

 mine in liquid ammonia, as recommended by Jacu- 

 bowitsch.* Similar sections may be made of ganglia 

 hardened in chromic acid ; and very minute speci- 

 mens of ganglia are sometimes immersed in potash 

 and moderately compressed between two slips of 

 glass. 



Nervous centres. The arrangement of the elements of nerve-tissue, 



throughout the cerebro-spinal centres, is far from 



spinal marrow, being clearly made out. The spinal cord consists of 



a central mass of grey matter, surrounded on all sides 



by white matter. The latter is made up almost 



wwte substance- exclusively of nerve fibres, with some blood-vessels, 

 supported by scanty and delicate connecting tissue. 

 By the aid of transverse and longitudinal sections, 

 we can see that some of the nerve fibres run parallel 

 with, and others perpendicular to, the axis of the 

 cord. The former constitute the greater proportion 

 of the white substance, and are found everywhere ; 

 whilst the latter are only to be seen where the roots 

 of the spinal nerves become continuous with the sub- 

 stance of the cord. It is to be noted also that the 



* Jacubowitsch and Owsjannikow are connected with one of the Russian 

 Universities, and published their researches on the nerves in the Bull, de 

 1'Acad. de Petersbourg, classe k phys.-^Mathem., torn. xiv. No. 323, 

 page 173. (Ed.) 



