STAINING, PRACTICAL AND THEORETICAL 



6. Transfer to a mixture consisting of equal parts of paraffin 

 wax and pure benzene in the embedding oven for an hour. 



7. Immerse in two changes of pure paraffin wax from a quarter 

 of an hour to six hours in each, depending upon the thickness and 

 the nature of the tissue. 



Note: It is of utmost importance that tissues should be kept in 

 the embedding oven just long enough for the paraffin wax to 

 penetrate fully. Prolonged heating in the oven causes shrinking 

 and hardening of the tissues rendering sections difficult to cut. 

 If, on the other hand, any of the Methyl Benzoate remains in the 

 tissue and sufficient time has not been allowed for proper pene- 

 tration of the paraffin wax satisfactory sections cannot be cut. It 

 is best, whenever possible, to cut thin slices of tissue for embedding, 

 preferably not more than 5 mm. thick so that the total time for 

 impregnating in the pure paraffin wax need be no longer than 

 three hours. Large objects such as whole embryos need a total 

 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 500). 



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. 



490 



