NERVOUS CENTRES GANGLION-CELLS. 295 



grey ; but we find there a translucent connective sub- 

 stance, pervaded by a large number of delicate vessels, 

 and assuming, in proportion as these are more or less 

 full, at one time more a reddish grey, at another more a 

 whitish grey hue. On the other hand it frequently hap- 

 pens that, where there are ganglion-cells, the substance 

 really does not look grey, but has a positive colour vary- 

 ing between brownish yellow and blackish brown. Thus 

 we find spots in the brain, which have long been known 

 by the names of substantia nigra, fusca, etc., in which the 

 black or brown colour, which we perceive with the naked 

 eye, is dependent upon the ganglion- cells, which form 

 really coloured points. 



This coloration appears only in the course of years. 

 The older an individual becomes, the more conspicuously 

 do the colours show themselves ; still under certain cir- 

 cumstances pathological processes also seem to accelerate 

 their manifestation. Thus in the ganglia of the sympa- 

 thetic it is a striking phenomenon, that certain morbid 

 processes, for example, typhoid fever, appear to exercise 

 a powerful influence in producing an early deposit of pig- 

 ment. Since the pigment however constitutes a rela- 

 tively foreign mass in the internal economy of the gan- 

 glion-cells, and is not, as far as we know, subservient to 

 their proper functions, but has all the characters of an 

 inert accidental deposit, it may really be quite possible 

 that these conditions should be regarded as a kind of 

 premature senescence in the ganglia. In these cases we 

 discern in the ganglion- cells (Fig. 88, a) in addition to the 

 very distinct, large nucleus with its large, bright nucleo- 

 lus, the contents properly so-called, which consist of a 

 finely granular substance, and at a certain spot enclose 

 the pigment which is generally deposited excentrically, 

 but sometimes around the nucleus. Under certain cir- 

 cumstances this deposit increases to such an extent that 



