Dear Katharina:

I have heard Delesse’s principle of areal analysis invoked to justify using point counting on thin sections to estimate area and then translating the area to volume by multiplying the area estimate by the section thickness and the section interval. You are asking about the Area Fraction Fractionator (AFF) to get a percent by volume estimate of a certain phase of the tissue. You have the idea right, the AFF works by dividing the points you put down on the phase whose percent by volume you are estimating by all the points that go on all the tissue. It will give you an estimate of percent by volumeof a given phase of the tissue, and as you say, if you want to know the absolute volume of that phase, you multiply the area fraction by the total volume.