ABSTRACT
This chapter discusses the percentages of selected lesions in rats that died as part of the aging study with the percentage of lesions in rats killed at two ages, namely, 14 and 21 months. Comparisons will be based on three types of findings, namely, the percent of lesions in dead rats during each age period, the age-associated percent based on the population at risk during each age period as calculated by life table techniques, and the percent in rats killed at specific ages. The real incidence of a lesion in the living population can be determined only by killing animals at specific ages. As the population aged, the risk of a rat dying with a medullary thyroid tumor increased and the percentage of rats dying with these lesions also increased. The organs examined from the Wistar-derived (WAG)/Rij females included pituitary gland, thyroid glands, adrenal glands, mammary glands, and liver.
