SECTION ONE 



7. Transfer to 4% Celloidin for five to seven days. 



8. Impregnate with 8% Celloidin for three or four days. 



9. The tissue is then taken out of the Celloidin and put into a 

 mould made by folding a piece of writing paper, and the whole is 

 then placed in a desiccator and left for several days, lifting the 

 desiccator lid for a few seconds each day to accelerate the harden- 

 ing of the Celloidin. If, through shrinkage of the Celloidin during 

 this process, the tissue becomes exposed, pour on more Celloidin 

 solution to cover it. Hardening of the block may be hastened by 

 placing 1-2 ml. of chloroform in the bottom of the desiccator. 



The block is hard enough for sectioning when no impression is 

 left after pressing with the ball of the thumb. 



10. The base of the hardened Celloidin block is dipped into 8% 

 Celloidin then fixed to a roughened wooden or a vulcanite block by 

 pressing firmly, afterwards leaving for at least half an hour with a 

 weight on top. 



11. Expose to chloroform vapour for half an hour; then attach 

 the wooden or vulcanite block to the microtome holder, or store 

 the Celloidin block mounted on the wooden or vulcanite block in 

 80% alcohol until required for sectioning. 



12. The microtome knife and the Celloidin block must be kept 

 moist with 70% alcohol and each section as it is cut must be trans- 

 ferred by means of a camel-hair brush, moistened with 70% 

 alcohol, into a suitable vessel containing 70% alcohol in which the 

 sections can be stored indefinitely until required for staining. 



13. When required for staining the sections should be removed 

 from the 70% alcohol by means of a small camel-hair brush, or a 

 piece of thin glass rod bent at one end, and transferred to a series of 

 watch glasses containing the reagents and stains, arranged on the 

 bench in the order in which they are to be used. For instance, if it 

 is desired to stain the sections with Haematoxylin and Eosin, the 

 steps are as follows : 



14. Immerse sections in 50% alcohol for a few minutes; then 

 transfer to water. 



15. Stain with Ehrlich Haematoxylin by the standard technique. 



16. Blue in tap water ; then stain in Eosin (aqueous solution). 



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