Abstract
Accruing acceleration in the rate of growth and development occurs in young rats when successive generations of parents rats are given daily intraperitoneal injections of 1 cc. of potent thymus extract (Hanson) (1). It would seem likely that, if an excess of thymic tissue or extract or over-activity of the thymus results in acceleration in growth and development in the young, the removal of the gland from successive generations should result in retardation in the rate of growth and possibly a retardation in the rate of development of the offspring. With this in mind, 5 pairs of rats (Wistar strain) of known parentage were selected from the normal stock animals of the Philadelphia Institute for Medical Research. One pair was thymectomized on October 10, 1934, and 3 pairs on December 14, 1934, all at the age of 21 days. On the latter date a fifth pair was subjected to a similar operative procedure except that the thymus gland was not removed. This pair constituted an operative control.
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