98 NOTES AND MEMORANDA. 



drops. From the manner in which these escape and hecorae 

 detached, Boll thinks it most probable that the axis-cylinder 

 is provided with a special sheath of its own. 



c. — Nerve Fibre in Picrocartnine and Concentrated 

 Picric Acid. 



If nerve be teased in a drop of concentrated picrocarmine 

 the medullary sheath becomes very soon of a greenish-yellow 

 tint. During the progress of the coloration similar results 

 are produced to those effected by distilled water, but more 

 slowly. The medullary sheath swells and becomes wider, 

 its segments become fused together, and finally it becomes 

 laminated, but does not liquefy. The axis-cylinder becomes 

 tinted red, but very slowly, hours, and even days, being 

 necessary for completion of the process. It then appears as 

 a homogeneous red filament of nearly uniform breadth. 

 Concentrated picric acid acts on the medullary sheath in 

 quite the same way as picrocarmine, but more energetically, 

 the nerve fibres being almost immediately coloured yellow. 

 The medullary segments become fused into a continuous 

 mass, but this, instead of being laminated, has a more or 

 less granular appearance. The axis-cylinder appears as a 

 filament of uniform breadth. 



D. — Nerve-Jibre in Osmic Acid. 



If nerve fibre be teased in 1% solution of osmic acid, the 

 first changes are that the medullary segments become brown 

 and broader than before, nearly double their previous breadth. 

 At the same time they lose their brilliancy and homogeneity, 

 becoming granular and turbid. By a longer action of the 

 reagent, the medullary sheath becomes darker and darker, 

 and folded upon itself, forming longitudinal and transverse 

 wrinkles. The medullary segments lose their sharp edges, 

 and afterwards become completely fused together. If small 

 nerves be examined after being kept for days or weeks in 

 osmic acid, we find the medullary sheath of an inky -black 

 colour, and the transverse diameter of the nerve fibres is 

 invariably diminished ; they look dessiccated, and have evi- 

 dently lost a considerable quantity of water. This shrinking 

 must be chiefly produced at the expense of the axis-cylinder, 

 as the medullary sheath appears dilated and granular, and 

 usually much wrinkled and folded. The medullary segments 

 can usually still be recognised as distinct, but so altered that 

 the discontinuity might easily be attributed to accidental 

 lesions in the process of hardening. If nerve be treated 



