STAINING, PRACTICAL AND THEORETICAL 



are not translucent or transparent they should be left in the clearing 

 agent until they have reached that stage. 



(c) Embedding 



Technique: 



1. Transfer the object from the clearing agent to a mixture con- 

 sisting of approximately equal parts of paraffin wax and the clearing 

 agent in a tube and place the whole in the oven set at a temperature 

 from about 50 to 60° C. for one half to sixteen hours, depending upon 

 the size and nature of the object; half an hour is sufficient for 

 objects up to 3 mm. thick; an hour for 5 mm,, two hours for i cm., 

 and from eight to sixteen hours for bulky specimens such as whole 

 embryos. 



2. Transfer to pure paraffin wax in the oven from a quarter to 

 eight hours. 



3. Transfer to another bath of pure paraffin wax for the same 

 length of time. 



Note: Specimens up to 3 mm. thick usually require half an hour 

 in each of the two baths of pure paraffin wax, while specimens 

 5 mm. in thickness require about an hour; and i cm. about four 

 hours; very bulky objects about eight hours in each of the two 

 baths of wax. 



Pathological material containing thrombi, emboli, etc., striated 

 and non-striated muscle, organs containing a large amount of 

 blood (spleen, etc.), and fibrous tissue should be subjected to im- 

 mersion in the embedding baths for the minimum time necessary 

 for the wax to penetrate thoroughly, as they are particularly liable 

 to hardening and shrinkage when exposed to heat for prolonged 

 periods. 



Casting the Paraffin Block 



1. Smear the inside of the embedding angles and the embedding 

 base-plate very thinly with liquid paraffin; then adjust the angles 

 on the plate to form a mould of a suitable size. 



2. Fill the mould with molten paraffin wax; then place the 

 object in the wax and arrange it so that it is set in the right plane 

 for sectioning. 



3. When the wax block so formed is partially set, immerse it 

 gently, while still in the mould, in cold water to ensure rapid 



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