Casting block 



PARAFFIN SECTIONS 



101 



Fig. 42. Folding a cardboard box — (continued), d. Kdije of the fold in folded back over the 



creased corners. 



Fig. 43. Folding a cardboard box — {continued), e. Box is opened and the corners pinched. 



Fig. 44. Folding a cardboard box — (continued), f. Finished box. 



a rough guess, it may be said that a block 

 of hver tissue of three-to-five-millimeter 

 side will be satisfactorily impregnated 

 with wax after 30 minutes in each of three 

 baths, while a 96-hour chicken embryo will 

 require at least two hours in each of three 

 baths for its successful impregnation. 



While the object is being impregnated 

 with the wax it is necessary to decide what 

 type of vessel will be used to cast the final 

 block. This will depend more on tlie size 

 of the object than on the preference of the 

 worker. Very small objects may be most 

 satisfactorily embedded in ordinary watch 

 glasses (that is, ordinary thin-walled 

 watch glasses not Syracuse watch glasses 

 of the laboratory type) or in any other 



thin-walled glass vessel. Very large objects 

 are often embedded with the aid of two 

 thick L-shaped pieces of metal, which by 

 being slid against each other may be 

 caused to form a rectangular mold of vary- 

 ing dimensions. The writer himself regards 

 these as very clumsy, and always prefers 

 to prepare a cardboard or paper box than 

 to endeavor to maneuver metal molds 

 which are always getting jarred out of 

 place at the wrong moment. The prepara- 

 tion of a paper or cardboard box is easy; 

 the method preferred by the writer for 

 large boxes is shown in Figs. 39-44. 



Take a rectangular sheet of thin card or 

 stout paper approximately twice as long 

 as it is wide. The area of the floor of the 



