Thanks to all who responded to my post, I will certainly be trying out a
combination of the recommendations to see if I can 'clear' the problem.  I
have included some of the ideas sent to me. Thanks again, 

Debbie Faichney
Institute of Aquaculture
University of Stirling
Scotland

1.	Could your racks be contaminated?  
	Do you wash and dry them thoroughly after each day?  Are your slides
dry when
	you put them in xylene?  
	Also try two changes of xylene 5 min each. 


2.	Are all your fluids at the same level? It sounds like possibly water
is on
	the top of the slides and is not rinsed off going through your
alcohols then
	it goes into your xylene. This does sound like an issue of water
getting
	into your xylene. Do you use recycled alcohols and/or xylenes? If so
maybe
	they are not distilled properly


3.	Wherever the water is 
	coming from....be it atmospheric or just from not changing alcohols
frequently 
	enough...it is the water that causes Xylene to turn milky (and forms
the 
	droplets you describe as well). 


4.	Surely this has to be due to water carried into the
	xylene because the last alcohol wasn't 100%. Two
	possible causes suggest themselves:
	1. Insufficient shaking off of solvents (alcohols)
	during the steps of dehydration of the stained
	slides.
	2. Contamination of your supposedly absolute alcohol
	with water. Test for this by mixing some with new
	xylene. It shouldn't go milky. This fors the basis of
	a very simple assay for water in alcohols: 
	Hall, J (2001) A simple, rapid method for measuring 
	the percentage of water in alcohols used for
	dehydrating tissues. Biotech. Histochem. 76(1):41-42.

	> The second and subsequent rack/s of
	> slides can often clear perfectly. 

	Could it be that the xylene now contains enough alcohol
	to prevent milkiness when more small amounts of water
	are carried over into it?  If this is the case, you
	will probably see microscopic droplets of water in
	the mounted preparations, even though they look
	transparent to the unaided eye.

5.	How humid is your air??Exposing the rack/slides to air, the alcohol
(100%, I
	assume it IS a 100%) will pick up moisture and your Xylene will turn
cloudy.

	

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