On a system of fibre-cells. 535 



ments, wliich allow of a classification of the latter into a system of 

 a) Protoplasmic cell-elements and h) Fibre-elements as was proposed by 

 the writer on morphological, physiological, aetiological, and pathological 

 grounds (B. M. J. July, 28^^ 1893). 



In the present investigation the neuroglia fibre-elements claim 

 attention for it is out of these that a perivascular, condensed, feltwork 

 is formed, ensheathing the blood vessels of the Brain, forming a distinct 

 and well organised Fourth coating composed in a definitely arranged^ 

 way, of definite fibre elements, and presumably possessed therefore of 

 a definite function. 



The general network of neuroglia -fibres throughout the Brain 

 (cortex and medulla) would seem to form a fine diifuse feltwork, which 

 however exhibits special condensation in two regions, viz: 



a) In the surface of the Brain (see Fig. 7) which may be called 



the surface condensation system, and 

 h) Around the blood vessels of the Brain — the perivascular 



condensation system — the subject of the present paper. 

 In the rest of the Brain substance the network is generally dif- 

 fuse and non-concentrated. 



A classification of the Neuroglia system will suffice to make these 

 distinctions clear, and to enable their precise relation to be better 

 apprehended. The classification proposed is found in the authors paper 

 — British Medical Journal (July 28*»^ 1893). 



a) Protoplasmic elements — cells of mesoblastic origin — of 

 active lymphatic function — generally stellate and dendritic 

 in structure — mossy and granular in surface appearance. 



These are aggregated especially in the gray matter, and 

 consist of 



1^*- Large cells, attached to the adventitial sheath by "vas- 

 cular" protoplasmic thick processes. 

 2'^*^- Small cells immediately surrounding the bodies of the 

 larger nerve-cells of the cortex (pericellular elements). 

 h) Fibre elements — epiblastic in origin — sustentacular and 

 passive in function — forming both a diffuse network, and con- 

 densation systems. 



