134 



NERVOUS TISSUES 



i/f/iro/ilaxiH of Schiefferdecker or a~roi>laxni, as containing the active 

 conducting substance of the fiber. 



According to Verworn, Lenhossek and R. Goldschmidt, these elemen- 

 tary fibrillse (axon fibrils) in the axis cylinder are nothing else than 



skeletal substance for the 

 support of the semi-fluid 

 neuroplasm. The circum- 

 stance that many of the 

 fibrils of an axis cylinder 

 may be sectioned without 

 diminution of the maximum 

 effect of stimulation favors 

 the view that the neuro- 

 plasm is the essential con- 



FIG. 146. A SMALL PORTION OF A TRANSECTION 

 OF THE SCIATIC NEEVE OF A DOG. 



Nerve fibers are seen in transection; their 

 myelin sheaths are black, their neuraxes un- 

 stained. Osmium tetroxid. Photo. X 700. 



ducting substance. 



Tashiro has demon- 

 strated that a living nerve 

 gives off a definite amount 

 of carbon dioxid, and that 



when the nerve is stimulated the amount of carbon dioxid production is 

 increased. He conceives of the propagation of nerve impulses as a chemi- 

 cal change, the propagation being in 

 essence a restoration of equilibrium 

 in the nerve fiber disturbed at the 

 point of contact. 



The axis cylinder is, under certain 

 conditions at least, found to be in- 

 closed by an extremely delicate mem- 

 brane, the axolemma of Kiihne. The 

 existence of this membrane as an in- 

 tegral part of a living axis cylinder 

 has been denied by others. It may 

 be simply a fixation artifact. 



THK MEDULLARY SHEATH (\Yltile 

 Substance of tfcliwann, Mi/i'/i// 

 tf lira Hi). - The medullary slu-aili 

 forms a cylindrical investment for tin- 

 axis cylinder. Medullated fibers vary 



greatly in diameter according to the amount of myelin present. It 

 appears to be retained in position by the neurolemma, for when the 



FIG. 147. A GROUP OF LARGE MED- 

 ULLATED FIBERS FROM A NERVE IN 

 THE PERITRAOHEAL AREOLAR TIS- 

 SUE OF THE CAT. 



Ax, axis cylinder; Nk, neurokeratin 

 framework; Nc, neurolemma cell and 

 nucleus; M, medullary sheath; N, 

 neurolemma. X 1000. 



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