XVII, 2. Wilson: A new sj^stem of obtaining clirectfng-marks. 17;} 



are purely a matter of convenieuce and may be variecl at will ; Avhilst 

 a substantial accuracy of svirface is imperative. If a pair of accu- 

 rate embedding-bars are already in tlie possession of the worker, 

 the obvious plan is to make the quadrilateral outline on tbe base- 

 plate of such dimensions as will correspond with the embedding-bars 

 placed in position. 



Method: — Before proceeding to embed the object, the glass 

 base-plate is to be placed upou a snpport which will permit of its 

 belüg subsequently heated from below up to the meltiug point of 

 the paraftin. The base-plate and embedding-bars should be thoroughly 

 cleansed, though here there are, of course, no troublesome grooves 

 requiring careful treatment, as in the Born-Peter plate. The faint- 

 est trace of glycerin rubbed over after cleaning plate and bars, will 

 facilitate Separation of the paraftin block. 



One of the lengths of blackened and paraffin-infiltrated nerve- 

 strand may now be taken and laid carefully down, without bending 

 it, on a flat piece of glass. Two portions, of such a length as to 

 permit them to project slightly beyond the limits of the space en- 

 closed by the embedding-bars (thus about 2-5 cm long), are now 

 to be chopped off with a razor-edge, cutting vertically down upon 

 the glass surface. They are then to be lifted up, still without bend- 

 ing them, and laid down on the upper surface of the glass base- 

 plate, pushing them gently into position so as to bring them to lie 

 accurately coiucideut with tAvo of the parallel blackened liues visible 

 on the under surface of the base-plate, at either one, two or three 

 millimetres interval as may be preferred. More than two Strands 

 may, of course, be utilised if desired, but for most purposes the 

 sections of two Strands will prove quite adequate as directing marks 

 for the orientation of the wax plates. For certain simple cases even 

 one Strand may be sufficient, but as a rule two should be employed 

 to give proper security. 



Having placed the two Strands carefully in position over the 

 parallel lines chosen, the base-plate is now to be heated up from 

 below to the melting-point of the paraftin in order to temporarily 

 fix the Strands in position. And now is the time to rectify any 

 slight unevenness of the filaments caused by previous handling. 

 This is easily done by gently pushing with the point of a needle, 

 while the Strands lie tlaccid in the melted eondition, until their co- 

 incidence with the engraved parallel lines on the under surface of 

 the glass is quite perfect. 



