XXVII, 2. Wilson: Improved methods of utilising organised structures. 231 



II. 



An alternative method of utilising organised structures so as 

 to provide directing marks in paraffin blocks is a follows : — 



A plane glass plate is well cleaned , and then smeared with a 

 minimal amount of glycerine by means of the finger , as much as 

 possible being rubbed off so as to leave an apparently dry surface. 

 From a previously prepared block of bulk-stained tissue of a homo- 

 geneous character, like liver or cerebrum, very thick sections are 

 cut, e. g. of a thickness of, say, 50 microns. One of these sections 

 is transferred to the surface of the glass plate , a few drops of 

 water are run in under it, and the plate is then gently heated so 

 as to flatten out the section ; the water is then drained off and the 

 section allowed to dry on. A stock of prepared plates, with sections 

 thus mounted on thein, may be kept in store. 



When it is desired to embed for reconstruction purposes , all 

 that needs to be done is to set up ordinary Naples embedding bars 

 (of accurate rectangular construction) upon the glass plate so that 

 the previously-mounted paraffin section of tissue will occupy the 

 floor of the embedding chamber. (It is obvious that the dimensions 

 of the block of tissue providing the sections should be ample.) 



The object is then embedded in the usual way, and when the 

 Naples bars are removed from the congealed block a sharp knife 

 should be run round the glass plate close to the edges of the block. 

 If the block is not thus at once loosened, the plate, with the block, 

 should be placed in a vessel of water, when it will soon become 

 detached. There will thus be obtained a rectangular parafiin block, 

 one face of which will be constituted by a perfectly uniform layer 

 or wall of tissue , 50 microns thick. This face of the block must 

 now be grooved by means of a „Ritzer", after Keibel's method. 

 It is desirable that the grooves made by the „Ritzer" should not 

 be deeper than the thickness of the wall of the tissue forming the 

 side of the block. No further treatment is required, and the block 

 may be at once mounted on the microtome plate upon one of its 

 end surfaces with the usual precautions to ensure that the grooves 

 made by the „Ritzer" shall be truly perpendicular to the cutting 

 plane. 



Though this second method is perhaps in some respects the 

 readier method of the two described , the first method has the ad- 

 vantage of a deeper inclusion of the directing strands within the 



