STAINING, PRACTICAL AND THEORETICAL 



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). 



17. Transfer to 70% alcohol; then immerse for five minutes in 

 each of two lots of 96% alcohol. 



Note: Absolute alcohol must be avoided as Celloidin is dis- 

 solved by it. 



18. Immerse for five minutes each in two lots of Carbol-Xylol. 



19. Pass into two changes of xylol. 



20. Mount in balsam or D.P.X. 



{b) Dry Method 



1. Proceed exactly as described above up to and including step 

 No. 8 ; then take the tissue out of the Celloidin and put it into a 

 paper mould as described in step No. 9 (above). 



2. Place the block in a desiccator for a day, lifting the Hd for a 

 few seconds every hour or so; then leave in the desiccator over- 

 night. 



3. Next morning place the block in a mixture consisting of equal 

 volumes of cedarwood oil and chloroform and add another 8 vol- 

 umes of cedarwood oil, one volume at a time, every hour for small 

 objects, or every day in the case of large objects. The Celloidin 

 should now be wholly transparent. 



488 



