Retarded Growth, Life Span, Ultimate Body Size and Age Changes in the Albino Rat after Feeding Diets Restricted in Calories

Rats were retarded in growth for periods of 300, 500, 700 and 1000 days before being allowed to grow to maturity. Members of each of these groups were alive when the last of the control groups had died at an age of 965 days. Retardation of growth by diets, complete except for calories, affords a means of producing very old animals for studying aging. Animals that are retarded for even 300 days can never become as large as those that mature normally. After 1000 days of retardation only part of the rats were able to resume growth when adequate energy was allowed in the diet. Even at this extreme period the male tended to grow to a larger size than the female. The growth of the bones in rats retarded for 700 and 1000 days was followed by means of x-ray photographs. The maintenance of a constant body weight in this period of old age does not check the growth of the bones. These increase slowly and respond to realimentation in all cases after 700 days of retardation but in only part of the cases after 1000 days.