MEDICAL AND BIOLOGICAL STAINING TECHNIQUES 



time of twelve hours in pure paraffin wax. Pieces of brain and 

 spinal cord about 5 to 10 mm. thick, skin, and large objects such 

 as whole embryos need at least three changes of pure paraffin wax 

 for a total time of about 12 hours, whereas organs such as spleen, 

 containing a large amount of blood, muscle, fibrous tissue, require 

 no longer than a total of three hours in the paraffin baths. It is, 

 however, only by experience that the technique of embedding can 

 be mastered. 



8. Cast the tissue in an embedding mould and proceed as in the 

 case of paraffin sections {see page 32). 



CELLOIDIN - PYRIDIN 



A rapid method of dehydrating, clearing and embedding, 

 which obviates the use of alcohols and the consequent 



hardening of tissues 



Reagents required: 



A. Pyridin, extra pure, redistilled . . i volume 

 Celloidin 4% in equal volumes of 



absolute alcohol and ether . . i volume 



B. Celloidin 8% in equal volumes of 



absolute alcohol and ether. 



Technique: 



1. Pieces of tissue are fixed in the usual manner. 



2. Wash in running water for the prescribed time for the parti- 

 cular fixative employed. If a fixative containing mercury has been 

 used, remove mercurial precipitate by the standard technique. 



3. Immerse the tissue in two changes of Pyridin, from two to 

 eight hours in each, according to the nature and the thickness of 

 the tissue. 



4. Immerse for twenty-four hours each in two changes of a 

 mixture consisting of equal volumes of Pyridin and 4% Celloidin 

 (formula as above). 



5. Immerse in 8% Celloidin for twelve hours. 



6. The tissue is then removed from the Celloidin bath, blocked 

 and cut into sections by the standard technique described on 

 pages 19-20. 



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