Summer is in full force. Here in Texas that means I get to burn my fingers on the 120 degree steering wheel of my car each afternoon! And if that wasn't enough to remind me, I could tell because of the increased phone calls from customers asking, "Why is the Eosin bleeding from my sections after cover slipping?"
The answer may be tied to a growing trend of increased usage of xylene substitutes, especially in physician offices who wish to keep hazardous fumes from waiting patients. And while I can appreciate the logic behind the decision, you must know that xylene substitutes do not do a very good job of dealing with water. And when it is humid out, this can cause problems. You see, humidity not only plays havoc with your hair-do, it can also saturate your alcohols to the point where water may be left on the slides. After cover slipping, any residual water left on the slides allows the eosin to bleed out into the surrounding mounting media and leave your sections without a counter stain. Eosin likes water much more than alcohol so it is quite happy to "Go to the water". Of course, Murphy's Law always seems to rear its ugly head in the histology laboratory so you should not assume that all the slides will exhibit eosin bleed... just the most important ones or the ones that go to the most "picky" pathologist!
To avoid Eosin bleed when using xylene substitutes you may wish to use one station of xylene directly after the last alcohol. If you are a xylene free purist, then just rotate the alcohols more frequently. One other tip, gradually increase the levels of the absolute alcohol containers to the point that the last container completely covers the tops of the slides; this will eliminate those pesky drops hanging on the top of the slide, which eventually slide down and then create eosin free streaks in the tissues.
Xylene substitutes are here to stay and that is a very good thing from a health and safety standpoint. By eliminating some of the dangers, we can make the work place safer. But remember they may have an impact while humidity stays high. But "to all things there is a season" and soon the weather will get cooler and we will once again have pathologists who are happy with their Hematoxylin and EOSIN stained slides...now if I could only get my car to cool down!
