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



Portions of such bimdles of, say, 10 or 12 eentimetres in 

 lengtli, are to be suspended each by a thread tied to one end, at- 

 taching- at tlie same time to tlie other end a weight just sufficient 

 to keep tlie Strand perfectly straigbt, even wben immersed in fluid, 

 but witbout undue and uunecessary stretcbing. The pieces with the 

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



1 percent Solution of osmic acid in order at ouce to fix the nerve 

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

 in similar fashion through alcohols an xylol, and, still suspended 

 vertically, they are next to undergo Infiltration with paraftin in a 

 test-tube or other vessel in a paraffin oven. ^\"hen properly infil- 

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

 and allowed to solidify. There may thus be very easily obtained 

 a stock of lengths of perfectly straight nerve filaments which are 

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

 a straight condition until required. 



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

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

 bettungsrahmeu). The glass base-plate is of simpler construction 

 tlian the Born-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 ordinary use, but it should 

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

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

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

 surface a rectaugular quadrilateral outline, with sides measuring 



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 fouiul preferable to have them at alternating intervals 

 from one another of one and two millimetres, respectively. 



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

 augular throughout, and with plane surfaces, as with the method of 

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

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

 as above stated; but it may be pointed out that these dimensions 



