GEOGRAPHY AND THE PROPERTIES OF SURFACES. LAW AND ORDER IN THE HUMAN LUNG.

Abstract : Resin casts of the pulmonary artery and airway systems of the human lung were prepared and measured to branches of 0.8 mm in diameter. Branches were ordered according to Strahler's classification system for rivers, and geometric progression with order were observed for numbers of branches, diameter and length. Detailed analysis of the branching pattern suggests that the theory of mixed hexagonal hierarchies, previously applied to cities, rivers, trees and bovine livers, can also be applied in the lung. A new phenomonen, spatial competition or spatial sharing between adjacent branches is recognized. It was found that: Rd/RA = Ratio of diameters/Ratio of Areas = 1/2 for the airways and pulmonary artery, even though the value of Rd and RA differ between systems, and in the case of the pulmonary artery, between lungs. The reason for this remains in doubt, but may be related to minimizing work. Systems such as the human lung provide insights for geomorphologists on high order branching systems developed in an isotropic region, a condition seldom found on a land surface. (Author)