XVII, "2. Wilson: A now System of ubtuiniiig directing-iuarks. 171 



marks nre availahle in tlie object itself, it miglit not be possible to 

 supply tlie (loficiency by enibedding along witli it certain perf'ectly 

 straisilit organic filaments, since the modern techniqne of section- 

 mounting- enables ns to ensure tlie maintenance of the accurate re- 

 lative Position of sections of tliese to eacli other and to the sections 

 of the object to be reconstructed. 



Slender and elongated bundles or Strands of nerve fibres, fixed 

 and blackened in osmic acid, seemed likely to atford material ad- 

 mirably snited to the end in view. In order to utilise these, however, 

 it was esseutial 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 

 paraflin 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 fiUing up with 

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

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

 methods. It is claimed that these conditions are practically satisHed 

 by the procedure detailed below. 



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

 degree of inathematical straightness and exactitude attainable by the 

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

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

 genuine biological reciuirements, and it is open to question whether 

 the conditions of paraffin section-cutting 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 liere 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 pul)lication. 



Materials: — Some of the long aud 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 absenee 

 of any branching, aud their uniform calibre, in addition to their 

 delicacy, are features which render such Strands especially favourable 

 for the purpose. 



