PERINEURIUM AND NEURO-GLIA. 317 



be detected, which possess finely granular contents and 

 large granulated nuclei with nucleoli, and lie, certainly 

 in no very great number, between the nervous elements. 

 At certain spots it has indeed been hitherto impossible 

 to draw a well-defined boundary-line between the two 

 tissues, and especially so at the surface of the cerebel- 

 lum and cerebrum, between the granules which I have 

 already (p. 307) described to you as connected with large 

 ganglion-cells, and the nuclei of the connective tissue. 

 Wherever the parts are seen severed from their connec- 

 tions, it is not easy to make the distinction, and a posi- 

 tive decision is only possible as long as the parts are 

 viewed in their natural position. 



Now it is certainly of considerable importance to know 

 that in all nervous parts, in addition to the real nervous 

 elements, a second tissue exists, which is allied to the 

 large group of formations, which pervade the whole body, 

 and with which we have in the previous lectures become 

 acquainted under the name of connective tissues. In 

 considering the pathological or physiological conditions 

 of the brain or spinal marrow, the first point is always to 

 determine how far the tissue which is affected, attacked 

 or irritated, is nervous in its nature, or merely an inter- 

 stitial substance. We thus obtain at the very outset the 

 important criterion for the interpretation of morbid pro- 

 cesses, that the affections of the brain and spinal marrow 

 may sometimes be rather interstitial, at others rather 

 parenchymatous, and experience shows us that this very 

 interstitial tissue of the brain and spinal marrow is one 

 of the most frequent seats of morbid change, as for ex- 

 ample, of fatty degeneration. 



Within the neuro-glia run the vessels, which are 

 therefore nearly everywhere separated from the nervous 

 substance by a slender intervening layer, and are not in 

 immediate contact with it. The neuro-glia extends ir 



