Some effects of accelerating growth - I. General somatic development

Abstract By varying the number of rats to be suckled by a single mother from the first day of their lives, it has been possible so to accelerate the grow the rate of the animals in the small litters that they were two to four times heavier than those in the large litters when they were 21 days’ old. Although all the animals were offered unlimited amounts of the stock diet (‘Diet 41’) from the time they could eat it, the difference in size continued to increase and the animals from the small litters became much larger adults than the others, and remained so. By accelerating growth in this way the times at which anatomical, physiological and chemical maturity were reached were severally modified, and it was shown that the development of some functions such as ocular vision and eruption of the teeth was determined mainly by chronological age, while that of others such as sexual maturity was more closely linked with the attainment of a certain size. Chemical maturity of the skeletal muscles depended both upon age and size, and the muscle of the animals whose growth had been accelerated, even though large in size, showed some of the signs of immaturity to be expected from the chronological age.