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. 
Fic. 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. i 
Glycerine jelly requires heat but otherwise is used the same 
as gum arabic. Mr. Moseley found it very useful in studying 
the structure of A/7/epora and allied corals. 
