STAINING AND MOUNTING PARAFFIN SECTIONS 225 



3. Water (to remove the alcohol). 



4. Stain with haematin (or haematoxylin*) for ten minutes 

 or more, according to the nature of the specimen and the 

 condition of the stain. The exact length of time can only be 

 learnt by trial, but ten minutes will be about right. Rinse in 

 distilled water. 



5. Wash thoroughly in tap-water, continuing the washing 

 until the sections have a decidedly blue tinge. The 

 haematoxylin compounds are very much like litmus, being 

 red in presence of acids* and blue in presence of alkalies; the 

 sections are to be coloured blue, and the necessary alkali is 

 contained in the tap-water. It will hasten the process to 

 rinse them in a very dilute solution of ammonia, or, best of 

 all, a saturated solution of lithium carbonate. 



6. Stain in watery eosin for a minute or so. This is the 

 counterstain. The haematin will stain all nuclei blue, but will 

 scarcely tinge anything else; the eosin is added to stain other 

 structures a pale pink, and thus make them more visible. It 

 stains in about half a minute, 



7. Wash off the eosin under the tap. 



The sections are now stained. But they are opaque, and 

 not in a suitable condition to be examined under the micro- 

 scope, and are to be' rendered transparent by being mounted 

 in balsam. Now this cannot be done in the same ,way as was 

 used in the mounting of films, for the drying would cause 

 the sections to shrivel and obscure their structure. The 

 water is to be removed, it is true, but by the use of absolute 

 alcohol ; at least two lots should be used, and the slide rocked 

 from time to time. Then the alcohol (which will not mix 

 with balsam) is to be removed by the use of xylol, balsam 

 added, and the section covered with a cover-glass. The 

 remaining" steps are therefore : 



8. Absolute alcohol^ two lots (to dehydrate). 



9. Xylol, two lots (to render the section permeable to 

 balsam). 



10. Balsam and a cover-glass. 



The last three steps are practically the same as the first 

 three, but in the reversed order, and similar phenomena are 

 seen. The section is opaque whilst wetted with the alcohol 



* Delafield's haematoxylin is the best or ordinary work, and is best bought 

 ready made. 



15 



