SECTION CUTTING. 



127 



the accompanying figure. This is then made into a tray, the 

 diagonals coming on the outside of the ends and then the 

 portions which project on each of the shorter sides are folded 

 down, thus holding the whole securely. 



In case a section cutter with a hollow tube {e. g., the Ster- 

 ling microtome) be employed, it is better to embed directly in 

 the tube, the process being essentially the same. 



When soap is used for an embedding medium, the object is 

 soaked in water instead of turpentine and the soap is melted 

 with the addition of a slight amount of the same fluid. Other- 

 wise the process is the same as before. 



Fig. 38. 



The foregoing methods both require heat and with many 

 tissues as nerves, this produces an injurious effect. To avoid 

 this gum arabic is employed. The specimen is washed in 

 water and then placed in a thick mucilage of gum arabic and 

 water, and the whole immersed in strong alcohol. The alco- 

 hol extracts the water and thus coagulates and hardens the 

 whole. 



Glycerine jelly requires heat but otherwise is used the same 

 as gum arabic. Mr. Moseley found it very useful in studying 

 the structure of Millepora and allied corals. 



