STRUCTURE OF THE NERVE FIBRES. 



151 



ment, or from the whole soft fibre, and swim freely in the liquid 

 in which the preparation is contained, constituting the so- 

 called myelin drops (6). 



The medullary sheath, especially where it surrounds the axis 



Fig. 19. 



Fig. 19. Medullated nerve fibres 

 destitute of the sheath of Schwann, 

 recently removed from the fresh 

 spinal cord, a, two unaltered 

 fibres ; b b b, fibres in which the 

 medullary substance is swollen up 

 by imbibition into irregular drops 

 upon the surface ; b', a detached 

 drop of the same nature (a so- 

 called myelin drop) ; c, axis cylin- 

 der projecting from the medullary 

 sheath. 



Fig. 20. 



'/ I I 



Fig. 20. Medullated nerve fibre 

 invested by Schwann's sheath, 

 quite fresh, a, with a nucleus in 

 the sheath at x ; b, a very broad 

 fibre ; c, two very delicate and 

 closely approximated fibres ; d, a 

 fibre so changed by manipulation 

 that it exhibits the so-called co- 

 agulation contours. 



From the lumbar plexus of a 

 Frog. 



cylinder, as a somewhat thicker layer, changes after death, by 

 what may be termed a kind of coagulation, into a granular 

 semi-transparent mass. The changes proceed from without 



