170 Wilson: A new System of obtaining clirecting-marks. XYII, :i. 



]So Claim is here set up for any special originality in tlie con- 

 ceptioii of tlie method. Tliis is little more tliau a moditication. 

 tliough not a wliolly luiimportant one, of tlie improved method re- 

 cently described by Born and Petkr, ^ wliicli suggested itself to tlie 

 writer wliilst engaged in carrying out the Operations of the latter 

 method. 



The System of Boiix and Peter is without doubt very perfect 

 in its way. Its practica 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 producing npon 

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

 perpendicnlar to the proposed plane of sectiou. Such a plate may 

 not be readily procnrable by every worker. - But in an}^ case, its 

 ntilisation does not obviate the necessity for the further Operation of 

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

 pigment , and of iixing this layer by a subsequent process of lac- 

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

 amorphous pigment-layer which form the actnal directing-marks in 

 each section, and whose delineation upon the snrface of the wax- 

 plate forms the directing guide diiring the process of snperimposition 

 of the ciit-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 extraneons amorphous pigment to the paraffin block, are 

 coustituted by actnal definite 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 i)roximity to the 

 object to be sectioned and reconstructed, was suggested by the 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 runniug parts , if perpendicnlar to the sectional 

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



M Born, G. , u. Peter, IL, Zur Herstellung von Richtebenen und 

 Pichtlinien (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 rae by the assistant in the Physiological Laboratory of the Uni- 

 versity of Melbourne, who iinppens to be a very skilful glass-engraver. 



I 



