SIMPLE IMBEDDING. 137 



with the handle of a scalpel) than by excavation of material; the pith-cells- 

 that have been flattened and pushed to one side by the kneading tend to 

 regain their normal form and position during the soaking in alcohol, and 

 their resilience causes the imbedded object to be grasped with an often 

 surprising tightness. If the cylinder of pith does not fit the holder of the 

 microtome accurately in the dry state (which it should do if possible) it 

 should be wedged in by means of strips or thin wedges of kneaded pith 

 inserted dry, and the whole afterwards soaked. With well-hardened objects 

 this method, if skilfully carried out, allows of very accurate section cutting. 

 These processes are still sometimes employed ; in cytological researches, for 

 example (Flemming). 



Moist paper may be used for imbedding some objects. They should be 

 swathed in strips of printing paper softened in water, so as to form a roll 

 that will go home in the well of a cylinder microtome with a little pressure 

 (RiCHAEDSON, Journ. Roy. Mic. Soc., 1882, p. 474). 



Simple imbedding in a melted mass such as paraffin is per- 

 formed in one of the following ways. A little tray or box or 

 thimble is made out of paper, some melted mass is poured 

 into it ; at the moment when the mass has cooled so far as to 

 have a consistency that will not allow the object to sink to the 

 bottom, the object is placed on its surface, and more melted 

 mass poured on until the object is enclosed. Or the paper 

 tray being placed on cork, the object may be fixed in position 

 in it whilst empty by means of pins and the tray filled with 

 melted mass at one pour. The pins are removed when the 

 mass is cold. 



In either case when the mass is cold, the paper is removed 

 from it before cutting. 



To make paper trays, proceed as follows. Take a piece of 

 stout paper or thin cardboard, of the shape of the annexed 

 figure (Fig. 1) ; thin (foreign) postcards do very well indeed. 

 Fold it along the lines a a and b &', then along c c and d df , 

 taking care to fold always the same way. Then make the folds 

 A A', B B', C C', D D', still folding the same way. To f do this 

 you apply A c against A a, and pinch out the line A A', and 

 so on for the remaining angles. This done, you have an im- 

 perfect tray with dogs' ears at the angles. To finish it, turn the 

 dogs' ears round against the ends of the box, turn down out- 

 side the projecting flaps that remain, and pinch them down. 

 A well-made postcard tray will last through several im- 

 beddings, and will generally work better after having been 

 used than when new. 



To make paper thimbles, take a good cork, twist a strip of 



