The outlines of anatomy, physiology, and hygiene Being an edition of The essentials of anatomy, physiology, and hygiene, rev to conform to the legislation making the effects of alcohol and other narcotics upon the human system a mandatory study in public schools . FiG. 51.—Xene-fibers. 192 ORGANS OF CO-ORDINATION. parent material, which, after death, appears to co-agulate and becomes whitish and slightly is called the myelin, or, by others, the whitesubstance of Schwann, from the man who first de-scribed it. In the center of the whole runs a slen-der thread of transparent, very f
The outlines of anatomy, physiology, and hygiene Being an edition of The essentials of anatomy, physiology, and hygiene, rev to conform to the legislation making the effects of alcohol and other narcotics upon the human system a mandatory study in public schools . FiG. 51.—Xene-fibers. 192 ORGANS OF CO-ORDINATION. parent material, which, after death, appears to co-agulate and becomes whitish and slightly is called the myelin, or, by others, the whitesubstance of Schwann, from the man who first de-scribed it. In the center of the whole runs a slen-der thread of transparent, very finely granular mat-ter, called the axis-cylinder. This latter substance,in all probability, serves for the actual conductionof the nervous influence, whatever it may be, andthe white substance of Schwann, or myelin, proba-bly acts as an insulator. These distinctions be-tween the different portions of a nerve-fiber are notvisible in the living body, but are the result ofchanges which take place after the nerve has beenseparated from its connections, probably from asort of coagulation. 248. Nerve-Cells. — The gray matter does notconsist of fibers, but ofcells (Fig. 52) imbeddedin a mass of granular mat-ter. These cells vary in ?^TTTo 01. size from -^-^ to an inch in diameter, andeach contains a nucleusand nucleolus, usually verydistinctly marked. Eachcell also has prolonga-tions which extend fromits circumference in vari-ous directions, and are supposed in every instanceto connect either with a nerve-fiber or with someother cell. These prolongations vary in numberfrom one up to five or six, and, as they are tracedalong their course with the aid of the microscope, Fig. 52.—Nerve-cells. NERVE-SUBSTANCE. I93 they are seen to divide and subdivide until theybecome too small to follow. It is supposed thatevery nerve-iiber is connected with such a cell. The ncrvc-fibcrs, above described, constitutingthe white nerve-matter, are mere conductors of thencrvc-force. They constitute the
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