Lung morphometry: a fallacy in the use of the counting principle.

fallacy in the use of the counting principle. J. Appl. Physiol. 37(6): “95 1-954. 1974.-A two-dimensional morphometric analysis of human lung parenchyma was compared with findings on a three-dimensional reconstruction of the same portion of lung. With three-dimensional analysis, approximate increases in proportion of duct space by 20y0, number of alveoli by 8%, and number of ducts plus sacs by 600 % were calculated, indicating the presence of more than four generations of ducts plus sacs in normal human lung. The major error in the use of the morphometric counting principle is the counting of duct transections, as individual ducts do not have solid tissue boundaries between generations. The difficulty in the differentiation of alveolar from duct space and the use of inaccurate shape and distribution of size coefficients cause lesser errors. air spaces; alveolar ducts; alveolar-sacs; alveoli; lung anatomy; lung models; lung reconstruction; morphometry; stereology; transection IN 1962, WEIBEL AND GOMEZ (19) described a brilliantly derived new principle for counting tissue structures on random sections. This principle (17-20)) with other principles and methods (2, 11, 15, 16) based on the Delesse relationship that area1 proportions are equivalent to volumetric proportions (3), has been widely used in estimating the proportions, size, number, and generations *of pulmonary air spaces from examination of thin lung sections. Essentially, Weibel and Gomez (17-19) derived the formula N= n3/2