STAINING AND MOUNTING PARAFFIN SECTIONS I73 



8. Absolute alcohol — two lots (to remove the water). 



9. Xylol — two lots, or until the section becomes transparent. 



10. Balsam and a cover-glass. 



This method of staining is very easy of application, and the 

 results are exceedingly beautiful. Bacteria which take the stain 

 are coloured blue or violet, and actively dividing nuclei and 

 keratin are stained in the same way, while all other structures 

 are stained pink. 



III. Method for bacteria which do not stain by Gram's method, 

 suitable for sections of typhoid ulcers, lymphatic glands con- 

 taining plague bacilli, etc. 



The problem before us in this case is not at all easy of solution. 

 In the first place, the stains which colour the bacteria also colour 

 the tissues, especially the cell nuclei ; the bacteria are easy to 

 stain, but it is difficult to stain a section in which there is good 

 differentiation. In the second place, the stains which are used for 

 bacteria are all soluble in alcohol : but alcohol is used to dehydrate 

 the sections. The following method will be found to serve fairly 

 well in most cases, though it requires a certain amount of practice 

 for its successful accomplishment. 



I, 2, and 3. Xylol, alcohol, and water, as before. 



4. Stain in carbol thionin for ten minutes or a quarter of an 

 hour. 



5. Wash in running water for ten minutes or longer. This 

 removes the stain from the tissues before decolorizing the 

 bacteria, and a fairly differentiated specimen may be obtained if 

 the processes of staining and washing are carried out for suitable 

 lengths of time. 



Unna's polychrome methylene blue may be used in a similar 

 manner, and gives even better results. The staining should be 

 continued for about ten minutes, and decolorization effected by 

 very short immersion in dilute acetic acid (about J per cent.), 

 followed by a good washing in pure water. 



6. Remove as much water from the section as you can without 

 actually drying it by the cautious use of clean blotting-paper. 

 Then apply aniline oil until the section becomes perfectly trans- 

 lucent. Aniline oil mixes with water on the one hand and xylol 

 on the other, and can be used for dehydration just as alcohol 

 was ; the process is slower, and several lots of the oil must be 

 used. 



7. Wash off all the aniline oil by successive applications of 



