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Cycles were observed in thyroid content of radioactive iodide in cats and monkeys. The period of the cycles in cats was approximately 24 hours. In the 2 monkeys it was longer. The cycles occurred in both species after transplantation of the thyroid and persisted in the cat following division of the spinal cord in the lower cervical region. In 3 experiments on 2 decerebrate cats no cycles were found.
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Woods et al. (1966) studied this question.
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