. Compendium of histology. Histology. NERVE TISSUE. 195 fibres, as it does other fatty substances, here acts much less thoroughly and more slowly ; there must certainly, therefore, be a difference in the constitution of these two different fibrous substances. Our fine nerve tubes present an additional peculiarity. Every mistreatment, pressure, pulling or reagent to which it is subjected causes a certain displace- ment of the medulla, so that unnaturally thinned spaces interchange with rounded bulgings (e). The latter have been desig- nated as varicosities, and varicose nerve fibres are spoken
. Compendium of histology. Histology. NERVE TISSUE. 195 fibres, as it does other fatty substances, here acts much less thoroughly and more slowly ; there must certainly, therefore, be a difference in the constitution of these two different fibrous substances. Our fine nerve tubes present an additional peculiarity. Every mistreatment, pressure, pulling or reagent to which it is subjected causes a certain displace- ment of the medulla, so that unnaturally thinned spaces interchange with rounded bulgings (e). The latter have been desig- nated as varicosities, and varicose nerve fibres are spoken of. Nothing of the kind exists during life. We here touch upon another unsettled question. Ranvier, at present the first histologist of France, called attention to a familiar phenomenon, to constrictions which occur in the course of broad medullated (peripheral, but not central) fibres. Formerly, however, these con- strictions were always regarded as a product of the methods of preparation. Now, these constricted places (Fig. 171) are pretty regularly situated, and be- tween every two, very nearly at half the distance, one meets with a nucleus of the sheath of Svvann (a). It is thus in mammals, birds, and amphibia ; but in fishes the number of nuclei is greater between every two of these constric- tions. These Ranvier's " constriction rings," as the Germans have christened them, deserve—although we are at present far removed from an accurate knowledge of them—every consideration. The medullary sheath certainly isolates the axis cylinder ; but this medullary space permits the penetration of nutrient. Fig. 171.—Nerve fibres of the frog; a, after treatment with picro carmine: b, c, d, with osmic acid ; e, with nitrate of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Frey, Heinrich, 18
Size: 863px × 2896px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, bookpublishernewyo, bookyear1876
