XVII, "2. Wilson: A new System of obtaining directing-marks. 175 



Tlie einbeddiug-cliamber is now complete, witli the embedding- 

 bars in position enclosing- an embedding-area with plane glass floor, 

 across wliich there Stretch two perfectly straiglit Strands of blackened 

 nerve, fixed in position at eitlier end, and perfectly parallel to the 

 sides, and perpendiciilar to the ends, of the embedding-chamber. 



The process of embedding the object to be reconstructed may 

 now be carried out in the usiial way. The glass plate, however, 

 niust be heated up to the melting-point of the paraffin, preferably 

 by imniediate embedding after the previous heating, or by heating 

 np anew. Only two heatings of the base-plate are really uecessary, 

 viz. one to allow of the preliminary careful orientation upon, and 

 lixation to the base-plate, of the directing iilaments; and a second 

 to allow of the weighting and Hattening out, i. e. the permanent 

 tixation, of the ends of the directing Strands. It may be found 

 possible to combine these stages, by omitting the intermediate cooling, 

 but it is safer to have the filaments initially glued down before 

 attempting to more permauently secure the ends. 



The orientation of the object itself with reference to the direct- 

 ing Strands must of course be carried out after the embedding 

 Chamber is filled with melted paraffin ; and for this purpose the 

 base-plate may be trausferred to the glass stage of the dissecting- 

 microscope, as suggested by Born and Peter. The floor of the Cham- 

 ber must, however, remain warm until the orientation of the object 

 is effected. 



Subsequent cooling of the Chamber should be carried out rapidly 

 and cautliously by means of iced water; and cupping of the block 

 should be prevented as far as possible by careful additions of paraffin 

 drops and manipulation with heated needle. Regarding these raanip- 

 ulations nothing need be added to the Instructions of Born and Peter. 



By foUowing the directions above detailed a paraffin block is 

 obtained, the siirfaee of which (in contact with the glass base-plate, 

 and forming a „directing plane") has , embedded just beneath it, 

 two perfectly straight blackened Strands of nerve, with the object 

 itself embedded in very definite and intimate relations to these. In 

 this method a ,,directing-plane" becomes of little or no importance 

 once the directing filaments have been definitively laid down. What 

 remains of importance is the existence of two directing Strands at 



embedding-chamber, but otherwise gives rise to no real inconvenience. As 

 a practical measure the writer believes it, however, to be superfluous. 



