NOTES AND -MEMORANDA. 99 



■with a more dilute solution, e.g. '1%, we often obtain images 

 very closely resembling those produced by distilled water, 

 from which they are only distinguished by their brownish 

 colour, we again find a widening and swelling of the medul- 

 lary segments, which lose their brilliancy ; they then become 

 liquid and fused together into a frothy mass, which, after 

 prolonged action of the solution, becomes of a black colour. 

 The splitting takes place not only longitudinally, but in all 

 directions. Sometimes a special appearance is produced in 

 the altered medullary sheath of dark striae, at right angles 

 to the longitudinal axis of the medullary segments, which 

 then appear to consist of short and very delicate rods, ex- 

 tending from the axis-cylinder to the sheath of Schwann. 

 Lantermann, who first described these appearances, inclines 

 to consider them as the expression of natural structure ; but 

 Boll does not share his opinion, as no trace of rods can be 

 seen in the fresh sheath, and, moreover, it is not to be seen 

 in all osmic acid preparations. 



E. — Nerve Fibre in Chrojnate of Ammo7iia, 2%. 



McCarthy (' Q. J. M. S.,' 1875, p. 380) has described a 

 formation of rods as being displayed in the medullary sheath 

 by this reagent. Boll, however, in teased preparations in a 

 drop of this liquid found the results exactly the same as in 

 •75% salt solution, the changes of the axis-cylinder being 

 even better seen, as it takes a slightly yellowish tint. If 

 nerve be kept in the solution for several days, the fibres 

 shrink very much, and the medullary sheath, of which the 

 segments can no longer be made out, becomes wider and 

 irregularly striated ; but Boll could find no trace of rods. 

 He supposes that special conditions of diffusion must have 

 been set up in the larger anatomical preparations exposed to 

 the fluid bvMcCarthy, whereas he used only isolated nerves. 

 But as this reagent preserves perfectly for a long time the 

 characteristic image of fresh nerve, if much later any rod- 

 like structure should appear, it must be due to post-mortem 

 decomposition. 



r. — Nerve Fibre in Salt Solution, 10%. 



Immediately after making the preparation the medullary 

 segments can still be distinguished, but are no longer 

 separate, being fused by drops at their points of contact. 

 The whole nerve fibre appears occupied by a very large 

 number of very fine and strongly refracting granules, of 

 which it is impossible to determine whether they are placed 

 within the axis-cylinder or on its surface, or perhaps in the 



