610 



SUMIMARY OF CURRENT RESEARCHES RELATING TO 



crystallization dish. Since the dish containing the paraffin is raised from 

 the bottom the water flows under it, and soon solidifies the paraffin in the 

 lower part of the dish, which consequently holds the object fast. As soon 

 as a surface film is formed, enough water can be added to cover the 

 embedding mould to complete the hardening of the paraffin. In Petri 

 dishes or watch-glasses the bottom is practically flat and true, and the 

 tissue is allowed to sink to the bottom. When the tissue is cut out as 

 a block, the part that rested against the bottom makes one of the two 

 parallel sides, and requires little or no trimming. 



When a number of pieces of tissue or a number of series are embedded 

 in one disk of paraffin, it is dangerous to attempt to separate them with 

 a knife, as one can never be sure of the direction the crack in the paraffin 

 will take. The writer has found that a hand scroll-saw or coping-saw 

 does admirably for cutting a block of tissue from the main disk. The 

 use of the saw* permits many more pieces to be placed in the same space, 

 and no care need be taken to have well-defined pathways for the 

 paraffin to split along, as is necessary when a knife is used for separating 

 the pieces. 



New Embedding Stage.* — G. R. La Rue says the essential parts 

 of this embedding stage (fig. 42) are a transite base, 17f in. long by 



^CEJ. 



Fig. 42. 



J in. wide, mounted on three levelling screws, a copper stage made in 

 two parts, 4 by 18 in. and 4 by 4 in. respectively, and under one end 

 of the longer copper stage an electric heating unit. The heating unit 

 may be wound for any voltage and to yield any desired temperature. 

 No regulator or rheostat or other provision for controlling or varying 

 the temperature is provided, but since the coil is situated under one 

 end of the stage lower temperatures may be secured by moving the 

 object away from the coil. In practice the coil is attached to a con- 

 venient electric receptacle near the paraffin bath, and that part of the 

 stage over the coil is heated sufficiently to melt paraffin in a few 

 minutes. The embedding tray may now be warmed over the hot stage, 

 filled with melted paraffin and moved to a point on the stage where the 

 paraffin is kept just melted. Objects to be embedded are now transferred 

 to the embedding tray, oriented, and the label inserted at the end of 

 the tray with the legend towards the margin of the tray. Now the tray 

 is gently moved to the unheated end of the stage, where the paraffin is 

 permitted to congeal on the bottom sufficiently to hold the objects in 



* Trans, Amer. Micr. Soc„ xxxv. (1916) pp. 154-5 (1 fig.). 



