170 Wilson: A new systera of obtaining directing-marks. XVII, -2. 



xNO Claim is liere set iip for any special originality in tlie coii- 

 ception of the method. Tliis is little niore tliaii a modificatiou, 

 tliough not a wlioUy iinimportaut one, of the improved metbod re- 

 cently described by Born and Peter, ^ which snggested itself to the 

 writer whilst engaged in carrying out tlie Operations of the latter 

 method, 



The System of Born and Peter is without donbt very perfect 

 in its way. Its practice requires first of all the possession of a 

 plate of metal , or , preferably, of glass , provided with a series of 

 specially constructed grooves , for the purpose of prodncing upon 

 one face of the paraffin block a series of parallel ridges, accurately 

 perpendicular to the proposed plane of section. Such a plate may 

 not be readily procurable by every worker. - But in any case, its 

 utilisation does not obviate the necessity for the further Operation of 

 coating the directing plane and its ridges with a layer of extraneous 

 pigmeut , and of fixing this layer by a subsequent process of lac- 

 quering. It is, of course, the more or less serrated outlines of this 

 amorphous pigment-hiyer which form the actual directing-marks in 

 each section, and whose deliueation upon the surface of the wax- 

 plate forms the directing guide during the process of superimposition 

 of the cut-out plate-models. 



It is an advantage of the method now to be described , that 

 the lines of direction , instead of being generated by the superad- 

 dition of extraneous amorphous pigment to the parafnn block, are 

 constituted by actual detinite Strands of organised material embedded 

 in the substance of the paraffin block itself, and in the dosest and 

 most intimate relation to the object to be reconstructed. The poss- 

 ibility of utilising such Strands, embedded in close proximity to the 

 object to be sectioned and reconstructed, was suggested by tlie fact 

 of the sufficiency, for many of the more simple cases of reconstruct- 

 ion, of the intrinsic structures of the object itself as directing 

 guides, such as a tolerably straight notochord, or the contours 

 of various axially running parts , if perpendicular to the sectioual 

 plane. The question thus arose whether, in cases where no such 



1) Born, G. , u. Peter, H. , Zur Herstellung von Richtebenen und 

 Richtlinien (Zeitschr. f. wiss. Mikrosk. Bd. XV, 1898, p. 31). 



"-) A very fair glass plate, engraved with Born-Peter grooves, and 

 by means of which a very good ridged paraffin block is obtained, was 

 made for nie by the assistant in the Physiological Laboratory of the Uni- 

 versity of Melbourne, who happens to be a very skilful glass-engravor. 



