230 Wilson: Improved methods of utilising organised structures. XXVII, 2. 



base-plate, owing to their being forcibly jammed down at their ends 

 during the process of fixing the end-phitcs in position. Two pieces 

 of wire , of uniform calibre , (I use common pins with their heads 

 cut off), are now to be carefully inserted between the surface of 

 the base-plate and the nerve-strands, close to the end-plates. This 

 expedient serves to secure a slight uniform elevation of the strands 

 from the base-plate, and also to produce a very slight additional 

 tension. The amount of elevation will obviously depend upon the 

 calibre of the wire used for this purpose. All that now remains to 

 complete the embedding chamber is the provision of side walls. 

 These may be any convenient blocks of glass or metal. I have 

 found it, however, better to use blocks of the special form illustrat- 

 ed , <7, so as to secure a widely splayed aperture to the embed- 

 ding chamber. With a chamber having sloping sides the central 

 pitting or dimpling of the paraffin block during solidification is mini- 

 mised. 



If careful orientation of the object to be embedded is required, 

 the metal base-plate may be slightly warmed prior to embedding, 

 and the necessary manipulation carried out under a dissecting lens. 

 It is generally preferable in orientation of the object to allow it to 

 rest upon, or in close relation to, the nerve-strands. Owing to the 

 elevation of the latter from the surface of the base-plate they are 

 well within the surface of the rectangular paraffin block , and are 

 not merely embedded in its surface as in the earlier form of the 

 method. Their accuracy and reliability as directing marks is insured 

 by their parallelism with each other and with the surface of the 

 base-plate, and above all by their perpendicularity to the end-plates 

 defining the end surfaces of the paraffin block. 



It is one of these end surfaces which will form the future base 

 of the object-block. This surface is the only plane that retains its 

 importance after embedding has been accomplished, and the usual 

 precautions must be taken in mounting the object-block on the plate 

 of the microtome to ensure that this end-plane is strictly parallel to 

 the cutting-plane. 



I have found the method, as now described, extremely easy to 

 carry out, and perfectly reliable, provided the section-technique em- 

 ployed in the slide mounting be adequale to the purpose. 



