The embryonic and postnatal growth of rat and mouse. III. growth of the whole animal in the puberty, adult, and senescence phases in two inbred mouse strains (cpb-s and kba/2). Exponential growth, sudden changes in the growth rate, and a model for the regulation of the mitotic rate.
The growth model forumlated for prenatal and postnatal growth up to the middle of the puberty phase seems to be valid for the later postnatal phases as well, including adulthood and senescence. 2. In this model, growth consists of phases with exponential growth (constant specific growth rate) separated by sudden changes in the rate. 3. In the period described here, 7 phases can be distinguished, beginning with puberty (phase IV) and ending with senescence (phase X). 4. In 4 of these phases the growth rate does not differ significantly between the four groups of mice used. In the other 3 phases there are no differences between three of the groups but the fourth, one of the sexes of the CPB-S strain, differs very definitely from the rest. 5. Absence of growth occurred in some phases in one of the groups. 6. Some of the phases do not occur in all individual animals; this holds especially for phase VIII, which occurred in only about 25% of the animals. 7. The 'growth constants' postulated in Part I and now studied in the individual mice, tend to have a value of about 2. A theoretical model is described for the regulation of the mitotic rate giving 'growth constants' of about the same numerical value.
