134 



NERVOUS TISSUES 



FIG. 146. A SMALL PORTION OF A TRANSECTION 



OF THE SCIATIC NERVE OF A DOG. 

 .Nerve fibers are seen in transection; their 

 myelin sheaths are black, their neuraxes un- 

 stained. Osmium tetroxid. Photo. X 700. 



neuroplasm of Schiefferdecker or aacoplasm, as containing the active 

 conducting substance of the fiber. 



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

 tary fibrillae (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- 

 ducting substance. 



Tashiro has demon- 

 strated that a living nerve 

 gives off a definite amount 

 of carbon dioxid, and that 



when the nerye 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 Nk 



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 axolemrna 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. 



THE MEDULLARY SHEATH (White 

 Substance of Schwann, Alyelin 

 Sheath). The medullary sheath 

 forms a cylindrical investment for the 

 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 FlBERS FROM A NERVE IN 

 THE PERITRACHEAL AREOLAR TIS- 

 SUE OF THE CAT. 



Ax, axis cylinder; Nk, neurokeratin 

 framework; Nc, neurolemma cell and 

 nucleus; M, medullary sheath; N, 

 neurolemma. X 1000. ' 



