176 Wilson: A new System of (ibtaining directing-marks. XVII, 2. 



right angles to the eiids of the parallel-sided rectangular block, oue 

 of which euds is destined to form the base of the paraftin object- 

 block which is to be monnted lipon the prepared paraftiu-table of 

 the object-holder of the microtome. The cementing lipon the latter 

 of the basal plane of the object-block miist be eifected in such manner 

 as not to destroy the parallelism of the two snrfaces. A crucial 

 groove may be cut in one of the snrfaces to be apposed, and super- 

 heated paraffin riin in between the apposed faces in the mamier 

 recommended 1)y Born. Any trimming and recoating of the block 

 which may be necessary may now be carried out in the usual or 

 any desired way, so long as the directing Strands are preserved in 

 their original relations to the object. 



The foUowing advantages may be claimed for the method just 

 described : — (1) No special apparatus is required but such as is 

 presumably to hand in any biological laboratory. Even the glass 

 base-plate may be prepared hj means of the ordinary engraving dia- 

 mond if need be. (2) None of the Operations described requires 

 any special dexterity, and all of them may be successfully accom- 

 plished at once by any-one. The sureness and certainty of the 

 process are such that it is hardly possible to fail. (3) Yery little 

 extra expenditure of time is necessary beyond that required for or- 

 dinary embedding; that is, after a stock of prepared nerve has once 

 been laid in. So little extra time and trouble are implied that there 

 could be little objection to making the embedding of directing Strands 

 a routine procedure in the case of those classes of material for 

 which reconstruction may at any time turn out to be desirable. 

 (4) The actual directing marks in each section are brought as close 

 as may be chosen to the object, and may be in actual contact witli 

 it if that be desired. (5). Whenever the embedding has taken place 

 the importance of the directing plane disappears , the only plane 

 remaining of importance in the paraffin block being the future base 

 of the object-block. (6) The necessity is wholly avoided for any 

 scratching of the paraffin block by a ,, Ritzer", or for the alternat- 

 ive Born-Peter ridges. (7) There is no necessity for the filliug up 

 of Scratches or for the coating of ridges with amorphous colour, or 

 for any superaddition of colour, lacquer, or any foreign substance 

 whatever. (8) Each section bears its directing marks in the shape 

 of two (or more) circumscribed black spots possessing all the defin- 

 iteness and determinateness which belong to organised structiires. 

 (9) The directing Strands cause no iuconvenience during either pre- 



