THE EFFECT OF AGE, PREGNANCY AND LACTATION ON THE THYMUS GLAND AND LYMPH NODES OF THE MOUSE

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Abstract
SUMMARY: The behaviour of the superficial lymph nodes differs from that of the thymus gland during the various phases of life of the mouse. In male and female Strong A mice the thymus gland regresses with age, but the superficial lymph nodes do not. During pregnancy the thymus undergoes an accelerated temporary regression, but regenerates soon after the end of the lactation period (earlier in non-lactating post-partum females). The superficial lymph nodes show a lesser temporary regression which, however, does not become evident until after parturition. Their regeneration occurs after the lactation period, and after a corresponding period in non-lactating post-partum females. The difference in behaviour of the thymus and of the superficial lymph nodes is probably an indication of the greater sensitivity of the thymus to the increased output of adrenocortical hormones which occurs during pregnancy. Repeated injections of cortisone acetate into the intact animal induce a response in the thymus gland and superficial lymph nodes similar to that evoked by pregnancy.