172 Wilson: A new System of obtaining directing-marks. XVII, 2. 



Portions of sucli biindles of, say, 10 or 12 centimetres in 

 leugth, are to be suspeuded eacli by a tbread tied to one eud, at- 

 tacbing- at the same time to the other end a weigbt just sufficient 

 to keep the Strand perfectly straight, eveu wben immersed in fluid, 

 but witliout undue and uunecessary stretching. The pieces with the 

 weights attached are now to be hung up in a vessel containing a 



1 percent Solution of osniic acid in order at onee to fix the nerve 

 and to blacken the myelin of the fibres. They are then to be passed 

 in similar fashion tlirough alcohols an xylolj and, still suspended 

 vertically, they are next to undergo infiltration with paraffin in a 

 test-tube or other vessel in a paraffin oven. When properly infil- 

 trated, the vertical weighted Strands are to be lifted carefully out 

 and allowed to solidify. Tliere raay thus be very easily obtained 

 a stock of lengths of perfectly straight nerve fiiaments which are 

 rigid enough for careful handling, and these should be preserved in 

 a straight coudition until required. 



For the purpose of erabedding there are required a glass base- 

 plate and two of the usual Naples L-shaped enibedding-bars (Ein- 

 bettungsrahmen). The glass base-plate is of simpler coustruction 

 than the Borx-Peter plate and may without difficulty be constructed 

 in the laboratory from plane-surfaced glass. It may conveniently 

 be of such dimensions as to enable it to replace temporarily the 

 glass stage of the dissecting-microscope in ordinar,v use, but it should 

 not be more than 2 or 3 mm thick, in order to minimise parallax 

 in future procedure. It should liave plane surfaces, and it is con- 

 venient to have drawn or engraved on the central part of its upper 

 surface a rectangular quadrilateral outline, with sides measui'ing 



2 cm (i. e. similar to that on the Borx-Peter plate). This outline 

 should be blackened. On the under surface of the glass cor- 

 responding to the area enclosed by this outline, a series of deeply 

 engraved lines should be ruled and subsequently blackened. These 

 lines are to be accurately parallel to two of the sides of the quadri- 

 lateral figure on the upper surface, as well as to one another, and 

 it may be found preferable to have theiu at alternating intervals 

 from one another of one and two millimetres, respectively. 



The embedding-bars (of either metal or glass) must be truly rect- 

 angular throughout^ and with plane surfaces, as with the method of 

 Born and Peter. The length of their arms should correspond to the di- 

 mensions of the quadrilateral engraved ou the base-plate, i. e. 2 cm 

 as above stated: but it may bo pointed out that these dimensions 



