Experiments have shown that the survival period of thyrotoxic rats is markedly influenced by the environmental temperature, being of much longer duration at low than at high temperatures. Between 22° and 37.5°C., the relation of temperature to the survival period is approximately linear. The tolerance to relatively large doses of thyroid and thyroxine is considerably increased below 20°C., but is especially striking at 4–6° C.

Hyperplasia of the thyroid, which results from exposure to cold, may be prevented by the administration of desiccated thyroid or thyroxine.

The diminished concentration of creatine of the myocardium, which is a conspicuous finding in rats treated with thyroid substance, does not occur in physiological hyperthyroidism resulting from long continued exposure to a low thermal environment.

In rats kept at high temperatures, whether treated with thyroid substance, or not, there is apparently no storage of colloid in the gland. The significance of the relatively high values for heart creatine in these animals at time of death is briefly discussed.

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