XVII, 2. Wilson: A new System of (»btaining directing-marks. 175 



The embedding-cliamber is iiow complete, witli tlie embedding- 

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

 across which there Stretch two perfectly straight Strands of blackened 

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

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



The process of embedding the object to be reconstructed may 

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

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

 by immediate embedding after the previons heating, or by heating 

 up anew. Only two heatings of the base-plate are really necessary, 

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

 fixation to the base-plate , of the directing lilameuts ; and a second 

 to allow of the weighting and tiattening 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 permanently 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 transferred to the glass stage of the dissecting- 

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

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

 is effected. 



Subsequent cooling of the Chamber should be carried out rapidly 

 and caiitliously 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 manip- 

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



By foUowiug the directions above detailed a paraffin block is 

 obtained, the surface 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 intiniate relations to these. In 

 tliis method a ,,directing-plane" becomes of little or uo importauce 

 once the directing filaments have been definitively laid down. What 

 remains of importance is the existence of two directing Strands at 



embedding-chamber, but utherwise gives rise to no realinconvenience. As 

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



