STAINING AND MOUNTING PARAFFIN SECTIONS 171 



method suitable for the diagnosis of tumours, etc., and for 

 ordinary histological purposes ; (2) a method of staining to demon- 

 strate bacteria which stain by Gram's method ; (3) a method for 

 bacteria which do not stain by Gram's method; and (4) the 

 process for demonstrating tubercle bacilli in the tissues. 

 I. Staining sections for histological purposes : 



1. Xylol, two lots (to remove paraffin). 



2. Absolute alcohol, two lots (to remove xylol). 



3. Water (to remove the alcohol). 



4. Stain with haematein (or hematoxylin*) for ten minutes or 

 more, according to the nature of the specimen and the con- 

 dition 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 hsematoxylin 

 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 almost instantaneously. 



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 microscope, 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). 



* Delafield's hKraatoxylin is the best for ordinary work, and is best bought 

 ready made. 



