Asymptotic growth and complex allometry of the brain and body in the white rat.

A new four-parameter version of Pütter's growth curve (Pütter, 1920) is obtained by replacing time by a smooth non-negative function which incorporates an initial delay. Fitted through constrained iteratively-reweighted multiplicative least-squares, this curve provides an accurate description of asymptotic growth and complex allometry of brain weight and body length and weight in a cross-sectional sample of forty-four male white rats.