Thymus Weight in Relation to Body Weight in Castrated and in Adrenalectomized Rats

IT HAS BEEN observed in many species, that after puberty animals which have been castrated, adrenalectomized, or fed dessicated thyroid have larger thymus glands than their controls. These findings led some of the investigators to designate the larger thymus in the experimental groups as “hyperplastic” glands. Others preferred to refer to failure or retardation of the physiological “age involution” under such conditions (Hammar, 1936). It will be shown in this paper that this is a misconception. The thymus in such animals is neither un-involuted nor hyperplastic, but fails to undergo “accidental involution.” This statement finds support in Selye's observation that the atrophy of the thymus in the “alarm reaction” does not occur in adrenalectomized animals (Selye, 1940). The data on thymus weights presented below were obtained from male albino rats of the Sherman strain. The animals were killed and the thymus weighed on a microtorsion balance.