A study has been made of the pathological changes in the hearts and other tissues of animals rendered hyperthyroid with thyroxine. Forty-four rabbits and seventeen guinea pigs were given intramuscular injections of thyroxine every other day and sacrificed at varying intervals. Tissues from a series of normal animals (twenty guinea pigs and forty-three rabbits) were examined as a control. The changes in the heart and other tissues of hyperthyroid animals were insignificant and varied but little from changes seen in normal control animals. Of eight thyrotoxic guinea pigs that developed coincidental infection (bronchisepticus) all showed myocardial lesions. Of nine thyrotoxic guinea pigs, free of infection, only one gave evidence of myocardial change. It is pointed out that hyperthyroidism, per se, cannot be held responsible for these lesions, which would appear to have been associated with the infection.

It was noted that rigor mortis of the skeletal muscles occurred much sooner in the bodies of hyperthyroid animals than in normal animals.

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