Postnatal growth of the dog's bronchial tree.

Polyester resin casts of the bronchial tree were made from the lungs of four Labrador dogs which weighed 0.5, 3.4, 7.5 and 30.0 kg, respectively. The branching trees were ordered by the method of Strahler and plots made of number, mean diameter and mean length of branches in each order. The four length plots were found to lie parallel to each other, as did three of the four diameter plots. When data are divided by the cube root of body weight the length plots almost coincide, as do the diameter plots. This indicates that the bronchial tree grows in constant proportion to the cube root of body weight.