THE CIRCULATION OF CEREBRO-SPINAL, SUBSTANCE. 



563 



characterized by a suggestive feature: i.e., they occur, as far 

 as the neuroglia is concerned, in the elements adjoining the 

 blood-vessels or connected with them. Thus, Berkley writes: 

 "In the silver slides the support elements proper, so far as the 

 stain shows, present no variations from the control, but, on the 

 other hand, the vascular neuroglia gives indication that altera- 

 tions are taking place within its structures, and show consid- 

 erable variations from control preparations. The cell-bodies 

 are larger, the protoplasmic extensions are thick and knotty, 

 and the arms extending toward neighboring vessels are more 

 prominent than in the normal." As "the capillaries, like the 

 intermediary vessels, are tortuous and twisted," evidences of 

 intense engorgement, further emphasized by the "closely 

 packed" white blood-corpuscles found in the vascular lumen, 

 it seems but logical that the engorged capillary and the en- 

 gorged neuroglia-fibers should be continuous; otherwise the 

 latter neuroglia swelling would remain unaccounted for. 



Keferring to the spinal cord, Berdal 50 states that "the 

 moment the blood-vessels penetrate into the cord they become 

 covered, on a level with the perimedullary neuroglia layer, with 

 a coating of neuroglia, which follows them throughout all their 

 ramifications and accompanies them along their entire course." 

 Such a coating over cerebral capillaries would readily account 

 for the engorgement of both structures to which we have just 

 referred, since the channel, notwithstanding the alteration in 

 its external aspect owing to the assumption of an extra coat, 

 would, after all, be continuous. That such is the case is sus- 

 tained by the fact that in what has been termed "chronic 

 ependymitis" doubtless a condition in which the layer of neu- 

 roglia becomes permanently engorged a marked thickening of 

 the tissue occurs (0. Israel). The increase of blood in the 

 neuroglia-fibers which this morbid condition involves not only 

 coincides with the swellings observed by Berkley after various 

 forms of poisoning, but it is accounted for by the fact that 

 ependymal neuroglia-cells were found by Marchi to send "a 

 central extension which penetrates into the optic thalamus, 

 where it subdivides to become fixed upon the walls of the blood- 



Berdal: Loc. tit., p. 193. 



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