COMPARATIVE HISTOLOGICAL STUDY OF THE ADRENAL CORTEX OF THE WILD AND DOMESTICATED NORWAY RAT1

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Abstract
THE domestication of the wild Norway rat into the tame laboratory rat has produced striking alterations in temperament, anatomy and physiology (1). Because domestication involves obvious changes in the psychology of the animal the neuroendocrine system has received a large share of the emphasis in past studies which have sought to elucidate the role physiologic mechanisms play in domestication. The adrenals have long been known to show important differences between the wild and tame Norway rat. Watson reported in 1907 that the adrenals of the domesticated rat are smaller than those of the wild rat (2). King and H. H. Donaldson (3) and King (4) later found that in successive generations of wild rats bred in the laboratory the adrenals gradually become lighter and tend to approach the weights found in domesticated rats. J. C. Donaldson showed that the adrenal cortex accounts for the entire difference in size (5). This has been confirmed by Rogers and Richter (6).