LINING MEMBRANE OF THE CEREBRAL VENTRICLES. 3^ 



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 rendor 

 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 



