SPINAL CORD GREY MATTER -CENTRAL CANAL. 303 



times reddish grey colour. Wherever then the substance 

 appears white to the naked eye, it is essentially composed 

 of real, medullated nerve-fibres, in which only here and 

 there a few ganglion-cells are imbedded ; and indeed a 

 large proportion of these fibres are of considerable breadth, 

 so that the quantity of medullary matter is at certain 

 points extremely large. 



The grey matter of the horns is the real seat of the 

 ganglion-cells, but here too the grey colour is by no 

 means to be entirely ascribed to the accumulation of 

 ganglion-cells ; on the contrary, they never, as you will 

 afterwards see, form more than a small portion of this 

 matter, and the grey hue is chiefly due to there generally 

 being in these parts no separation of that opaque, strongly 

 refractive substance (myeline, medullary matter) which 

 fills the white nerves. 



It is in the centre of the grey substance that, as Still- 

 ing, especially, has shown, the central canal (canalis spi- 

 nalis) actually exists, which had previously been so com- 

 monly supposed to be present, and had also frequently 

 been described as of constant occurrence, but of which 

 nevertheless no one had ever previously been able to 

 furnish a regular demonstration. In the case of the old 

 observers, as for example Portal, their investigations were 

 in every instance confined to a few pathological speci- 

 mens, from which they derived all the information they 

 possessed upon the subject, and from which they inferred 

 in a somewhat arbitrary manner that the presence of a 

 canal was the rule. 



This central canal is so minute that extremely success- 

 ful sections are required in order that it may clearly be 

 perceived by the naked eye. Usually nothing more than 

 a rounded grey spot can be detected, which is distin- 

 guished from the surrounding parts by its somewhat 

 greater density. It is by microscopical examination 



