LINING MEMBRANE OF THE CEREBRAL VENTRICLES. 3H 



especially in the brain, this interstitial matter of ours was 

 regarded as essentially nervous, for a substance of the 

 kind appeared a natural desideratum, as long as a direct 

 transferrence of impulses from fibre to fibre was admitted 

 to take place, as long therefore as the necessity for a 

 real continuity of conduction within the nerves them- 

 selves was not recognized. Thus in the brain a finely 

 granular substance was spoken of as existing, which in- 

 sinuated itself between the fibres, and though it certainly 

 did not establish a complete connection between them, 

 inasmuch as it occasioned a certain difficulty in the trans- 

 ferrence of impulses, yet nevertheless seemed to rendc.r 

 a certain amount of conduction possible, so that when 

 the impulse reached a certain degree of intensity, a 

 direct transferrence from fibre to fibre could take place. 

 This substance is however unquestionably not of a ner- 

 vous nature, and if inquiry be made as to the relation 

 which exists between it and the familiar groups of physi- 

 ological tissues, it is impossible to doubt but that the 

 substance in question is a kind of connective tissue ; and 

 therefore an equivalent of that tissue with which we be- 

 came acquainted in the shape of perineurium (p. 265). 

 But the appearance of this substance is certainly very dif- 

 ferent from that of what we call perineurium or neurilem- 

 ma. These are comparatively firm, and often indeed hard 

 and tough tissues, whilst the substance in question is ex- 

 tremely soft and fragile, so that it is only with very great 

 difficulty that we can succeed in making out its structure. 

 I first had my attention directed to its peculiarities in 

 investigations which I many years ago (1846) instituted 

 into the nature of the so-called lining ' membrane of the 

 cerebral ventricles (Ependyma). At that time the view 

 was generally held, which had been put forward first by 

 Purkinje and Yalentin, and afterwards especially by 

 Henle, that a real lining membrane did not exist in the 



