318 LECTURE XIII. 



the peculiarly soft form, which it presents in the great 

 nervous centres and particularly in the brain, only to 

 those parts which must be regarded as direct prolonga- 

 tions of the cerebral substance, namely to the higher 

 nerves of sense. The olfactory and auditory nerves also 

 contain interstitial substance of the same character, whilst 

 in all the rest, and even in the optic nerve itself, an in- 

 creasing mass of a tougher tissue displays itself, which 

 assumes quite the character of perineurium. 



Perineurium and neuro-glia are therefore equivalent 

 jparts, the only difference being that the one is of a soft, 

 medullary, fragile nature, whilst the other is akin to the 

 well-known fibrous tissues. The neurilemma stands in 

 the same relation to the perineurium that the membranes 

 of the brain and spinal cord do to the neuro-glia. 



Wherever neuro-glia exists, a very singular peculiarity 

 presents itself which it has as yet been impossible to 

 explain either chemically or physically, namely, that in 

 every such case those peculiar bodies may be met with, 

 which even in their structure remind one of granules of 

 vegetable starch, whilst in their chemical reactions they 

 altogether correspond to them the much discussed cor- 

 pora amylacea (Fig. 94, ca). They are found to the 

 greatest extent and in the greatest numbers in the epen- 

 dyma of the ventricles and spinal canal, and are the 

 more abundant the greater the thickness of the ependyma. 

 In many places but very few of them are found, whilst 

 in others again their numbers increase so greatly, that 

 the whole thickness of the ependyma is filled with them 

 to such a degree, that it looks as if a pavement were be- 

 fore one. They display themselves, however, strangely 

 enough, in pathological conditions also, frequently in 

 great numbers, when, in consequence of some disturb- 

 ing cause, the quantity of neuro-glia becomes increased 

 in proportion to that of nervous substance, as for 



