  At the basic geometric level, the distribution networks carrying vital
materials in living organisms, and the units such as the nephrons and alveoli,
form a scaling structure named here the site model. This unified view of the
allometry of the kidney and lung of mammals is in agreement with the existing
data, and in some cases, improves the predictions of the previous fractal model
of the lung. Allometric scaling of surfaces and volumes of relevant organ parts
are derived from a few simple propositions about the collective characteristics
of the sites. New hypotheses and predictions are formulated, some verified by
the data, while others remain to be tested, such as the scaling of the number
of capillaries and the site model description of other organs.
