NER VE- TISSUE. 1 1 5 



teased apart longitudinally, in one-half-per-cent. salt so- 

 lution, care being taken to pull apart the fibres from the 

 ends, so as to break them as little as possible, and cov- 

 ered ; pressure from the cover-glass being avoided by 

 placing a bit of paper or hair beside the specimen. The 

 nerve-fibres present, if examined at once, in many parts, 

 a sharp and regular double contour, which is their normal 

 appearance, and along their course the constrictions and 

 nuclei may here and there be seen. The axis-cylinder 

 and neurilemma are for the most part invisible ; the for- 

 mer owing to the lack of transparency in the medullary 

 sheath, the latter because of its extreme thinness and 

 close contact with the medullary sheath. Very soon, at 

 once in some parts of the specimen, the contours of the 

 fibres will be seen to become irregular, the myelin 

 shrinking away at some parts from the neurilemma, and 

 swelling out at others. At the severed ends of the fibres 

 the myelin will be seen welling out from the neurilemma, 

 and breaking off into the fluid in irregular globular or 

 contorted masses. 



After the swelling and irregular breaking up of the 

 myelin has occurred this may be hastened by allowing 

 water to run under the cover-glass the neurilemma may 

 be seen here and there stretching across between the 

 varicosities formed by the swollen myelin, and either at 

 the broken ends of the fibres or along their course, the 

 axis cylinder may occasionally be seen. 



Nerve-Fibres Treated with Osmic Acid. The most 

 complete demonstration of the nerve-fibre may be ob- 

 tained by treatment with osmic acid. This agent fixes 

 the myelin and other constituents of the fibre nearly in 



