XVII, 2. Wilson: A new system of obtaining directing-inarks. 171 



marks are available in tlie object itself, it might not be possible to 

 supply the deficiency by enibedding along with it certain perfectly 

 straiglit orgauic filaments , since the modern technique of section- 

 mounting enables us to ensure the maintenance of the accurate re- 

 lative Position of sections of these to each other and to the sections 

 of the object to be reconstrncted. 



Slender and elongated bundles or Strands of nerve fibres, lixed 

 and blackened in osmie acid, seemed likely to attord material ad- 

 mirably suited to the end in view. In order to ntilise these, however, 

 it was essential to ensure the embedding of such Strands of tissue 

 so that they should be perfectly straight, perfectly parallel to one 

 another, and perfectly at right angles to the plane of section of the 

 paraffin block; — in short, to ensure the assimilation of the linear 

 disposition of such embedded Strands as closely as possible to that 

 of the parallel lines of colour which result from filling up with 

 pigment the parallel Scratches produced by a „Ritzer" on the face 

 of a paraftin block prepared for reconstruction by one of the older 

 raethods. It is claimed that these conditions are practically satisfied 

 by the procedure detailed below. 



It may be contended that it is impossible thus to obtain that 

 degree of mathematical straightness and exactitude attainable by the 

 use of the „Ritzer", or by the Born -Peter ridges. But there is 

 certainly to be gained a degree of accuracy amply sufficient for all 

 genuine biological requirements, and it is open to question whether 

 the conditions of paraffin section-cuttiug and mounting will permit 

 of substantially greater accuracy by any method whatsoever. 



For the rest it is sufficient to add that the practical value of 

 the method here advocated has been already borne out by actual 

 experience of its working. The simplicity and reasonableness of 

 its underlying principle, along with its practical convenience ad read- 

 iness, are held to justify its present publication. 



Materials: — Some of the long and slender root-bundles of the 

 human cauda equina will be found to be admirably adapted for the 

 purpose of embedding as directing-strands. The intraspinal roots of 

 the fifth sacral and coccygeal nerves are very long and fine, but. 

 if more delicate Strands are desired, it is quite easy to separate 

 finer individual bundles from other nerve-roots. The entire absence 

 of any branchiug, and their uniform calibre, in addition to their 

 delicacy, are features which render such Strands especially favourable 

 for the purpose. 



