Body size, energy metabolism, and the lungs.

The theoretical basis for applying the power function y = aMb to the study of structure-function relationships is discussed. Dimensional analysis and the distinction between intensive and extensive properties of animals show that the mass coefficient a represents the effect of intensive or qualitative factors on the considered function or structure. The theoretical mass exponent is a criterion for the constancy of a and the qualitative sameness of the compared structure or function. Examples from respiratory and metabolic physiology are given.