STAINS AND STAINING 51 



good nuclear stain, while at the same time it removes any disfiguring 

 precipitates. Some prefer to stain for a very short time and use no acid 

 alcohol, but, as a rule, it is better to overstain and then diHerentiate in 

 this way, because sharper contrasts are obtained. Transfer from acid 

 alcohol to 70 per cent alcohol and leave here until a rich purple color 

 replaces the red due to the acid. Since small quantities of the acid 

 alcohol are carried over into the 70 per cent alcohol, it is well to add a 

 drop of ammonia now and then to neutralize the effect of the acid. Too 

 much ammonia is to be avoided, for it gives a disagreeable bluish color 

 with poor differentiation, probably on account of the precipitation of 

 alumina. The preparation is now dehydrated in 95 per cent and then 

 in absolute alcohol, cleared in xylol or clove oil, and mounted in bal- 

 sam. 



The following is a general schedule for staining paraffin sections on 

 the shde in Delafields' haematoxylin : 



1. Stain (from water or from 35 or 50 per cent alcohol) 10 minutes 



2. Rinse in water 10 minutes 



3. Thirty-five and 50 per cent alcohol 3 minutes each 



4. Acid alcohol 5 seconds 



5. Seventy per cent alcohol 3 minutes 



6. Eighty-five per cent alcohol 3 minutes 



7. Ninety-five per cent and 100 per cent alcohol . . 3 minutes each 



8. Xylol and 100 per cent alcohol, equal parts 3 minutes 



9. Xylol 3 minutes 



10. Mount in balsam. 



If, after rinsing in water, the stain is evidently too weak, put the 

 slide or section back into the stain until it appears overstained. Place 

 the slide in acid alcohol. If an acid alcohol with 2 drops of HCl to 

 100 c.c. of 70 per cent alcohol reduces the stain too much in 10 or 15 

 seconds, use less acid or stain longer. Transfer to 70 per cent alcohol 

 without any acid. As soon as the color changes from red to purple, 

 examine under the microscope. If it is still overstained, return to the 

 acid alcohol ; if the stain is too weak, return to the haematoxylin and 

 try it again. After the haematoxylin is just right, apply a contrast 

 stain, if you wish to double stain. Before transferring to the xylol 

 wipe the alcohol from the back of the slide, or at least rest the corner 

 of the slide upon blotting-paper for 2 or 3 seconds, in order that you 

 may not carry over so much alcohol into the xylol. Add a drop of 



