1538 Journal of Applied Microscopy 



are lifted carefully out and allowed to harden, and can be kept till required for 

 use. 



For embedding, a glass base plate and the usual Naples L-shaped embed- 

 ding bars are required. The glass plate may be constructed in the laboratory 

 from plane-surfaced glass. It is convenient to have it of such a shape as to 

 replace easily the stage of a dissecting microscope, but it should not be more 

 than 2-0 mm. thick. The surfaces should be plane, and it is advantageous to 

 have a central, rectangular outline on the upper surface with the sides measur- 

 ing 2 cm. each. This outline should be blackened. On the under side of this 

 area a series of deep lines should be engraved and blackened ; they must be 

 accurately parallel to two of the sides of the quadilateral figure on the upper side 

 and to each other, and placed at intervals of 1-2 mm. The embedding bars 

 should be exactly rectangular throughout, and have their arms 2 cm. in length. 



Before proceeding to embed the object, the glass plate must be so placed 

 that it can be heated from below, and it and the bars are slightly rubbed with 

 glycerin to facilitate the removal of the paraftin block. Two or more of the 

 blackened strands of nerve tissue are laid very carefully on the glass coincident 

 with two of the parallel blackened lines. The base plate is now heated to fix 

 the paraffin-covered strands in place, and to arrange them perfectly coincident 

 with the engraved lines. One of the embedding bars is then so placed that the 

 cross-arm will limit the basal plane of the future paraffin block, corresponding 

 to or parallel to the plane of sectioning. Both bars slightly cover the ends of 

 the nerve strands. A moderate weight of a kilo, in the shape of an iron bar, is 

 laid on the upper surface of the embedding bars, and the plate is again heated 

 till the paraffin is melted, and either allowed to cool or the process of embedding 

 completed. The weighting of the bars allows complete flattening of the ends of 

 the strands of tissue, which are held in place by the bases of the bars, and hence 

 their very slight thickness does not interfere with the angle of the surface of the 

 bars. If there is objection to this process, the filaments may be held down by 

 two pieces of lead placed inside the bars. If the plate has been allowed to cool 

 it must be again warmed to the melting point of paraffin ; after filling the 

 chamber with melted paraffin the object must be carefully oriented, with refer- 

 ence to the lines and strands, under a dissecting microscope, if necessary, but 

 the plate must be kept warm till everything is completed. Rapid cooling in iced 

 water follows, with care to prevent cupping of the block by the addition of drops 

 of melted paraffin, and manipulation with a hot needle. 



The advantages of this method are : 1. No special apparatus is required be- 

 yond what is found in any laboratory, even the glass plate may be prepared by an 

 ordinary engraving diamond if necessary. 2. None of the operations require 

 any special dexterity, and all may be accomplished by anyone with certainty. 

 3. Very little expenditure of time is required beyond that of ordinary embedding 

 after the stock of prepared nerve is laid in. 4. The actual directing marks in 

 each section are brought as close as desired to the object. 5. Whenever the 

 embedding has taken place the importance of the directing plane disappears, the 

 only plane of importance being the future base of the object block. 6. The 

 necessity for scratching the paraffin block by a " Ritzer " or for the alternative 



