THE FROG. -257 



S. Treat with acetic acid : the striation rendered 

 very indistinct; oval nuclei made apparent 

 here and there in the fibre. 



f. Nerve-fibres. 



i. Tease out a bit of fresh nerve in 07 5 sodic chlo- 

 ride. Examine with a high power. 



a. Composed of well-defined fibres (white nerve 

 fibres] mixed with white fibrous tissue (d. i. a}. 



b. The appearance of the nerve-fibres: each has 

 a double contour, marked out by a curdled- 

 looking highly refractive border on each side. 



c. The structure of the nerve-fibres. 



a. The delicate structureless investing mem- 

 brane (primitive sheath); look for it on 

 bruised nerve-fibres or at the ends of torn 

 fibres. 



ft. The highly refractive border (medullary 

 sheath) within the primitive sheath. 



y. The central homogeneous axis (axis cylinder); 

 look for it projecting beyond the medullary 

 sheath of torn fibres. 



d. Treat a fresh bit of teased-out nerve with chlo- 

 roform : the medullary sheath will be dissolved 

 out, and the axis cylinder plainly seen. 



g. Nerve-cells. 



i. Take a sympathetic ganglion from a recently killed 

 frog: dissect out in normal saline solution and ex- 

 amine with -- obj. 



a. Among the pigment-cells, which are clustered 

 around the ganglion, will be seen numerous 



M. 17 



