Charles Manning child was an American zoologist who developed a theory of how the various cells and tissues in organisms are organized - by a gradation in the rate of physiological processes leading to relationships of dominance and subjection. In 1900, Child began a series of experiments on regeneration in coelenterates and flatworms. In 1910 he perceived that there is a gradation in the rate of physiological processes along the longitudinal axis of organisms. According to his gradient theory, developed 1911, each part of an organism dominates the region behind and is predominated by that in front. In general, the region of the highest rate of activity in eggs, embryos, and other reproductive parts becomes the main point of the larval form. Regeneration follows the same principle. ‘Senescence and Rejuvenescence’ is one of Child’s most famous and important works, in which he considers questions of senescence and rejuvenescence.