SECTION ONE 



corked flask or bottle. Shake well; allow the flask or bottle to 

 stand upright for an hour or so ; then leave it inverted for an hour, 

 afterwards leave it lying horizontally for a time; then stand it 

 upright again, and repeat the process at intervals throughout the 

 day and leave the bottle lying on its side overnight : next morning, 

 solution should be complete and it is only necessary to shake the 

 bottle well to ensure a homogeneous solution. 



Technique: 



1. Tissues are fixed and washed in running water, and any mer- 

 curial precipitate removed in the usual manner. 



2. Immerse for two hours in each of the following: 50%, 70% 

 and 90% alcohol. 



3. Transfer to absolute alcohol for two to sixteen hours. 



4. Immerse in Methyl Benzoate - Celloidin solution for twenty- 

 four hours, at the end of which time pour oflF the solution and 

 replace with a fresh lot in which the tissue should remain for a 

 further forty-eight hours : if the tissue is not now clear, transfer it 

 to a fresh lot of Methyl Benzoate - Celloidin solution for a further 

 period of seventy-two hours. 



5. Immerse in three changes of pure benzene, for four hours in 

 the first lot, eight hours in the second, and twelve in the third. 



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 



21 



