On the Control of the Level of Activity of the Animal Body

Abstract

1. Barcroft and Izquierdo(1931) have shown that the form of the temperature-pulse rate curve of the excised heart of the frog differs seasonally. The effects produced by endocrine substances and extracts of endocrine glands on the form of this curve have been investigated with a view to determining the nature of the seasonal change within the body. 2. When the heart of a winter frog is allowed to beat for some hours in Ringer solution, there is no alteration in the form of the curve. If the heart is that of a summer frog, there is a gradual alteration of the curve towards the winter form. It is concluded that, if the control of this change is endocrine, the organ responsible is more active in the summer. 3. Thyroxine, at a concentration equivalent to the possible change in the amount of the thyroid secretion in the circulation, transforms the curve given by a winter heart into the summer form, but has no effect on the curve of a summer heart. 4. Adrenaline, pituitrin, thymus extract and extracts of non-endocrine organs, such as muscle and salivary glands, have no effect on the form of the curve. 5. Insulin, in large doses, and a general extract of the pituitary have an effect opposite to that of thyroxine, altering the curve from the summer to the winter form. 6. It is concluded (1) that the control of this phenomenon is endocrine and (2) that the thyroid is the effective organ, by increase of its activity in the summer. Although the adrenal does not control the phenomenon investigated, it is not excluded that it may control other seasonal changes in the frog and other vertebrates. 7. Of several chemical substances related to thyroxine, des-iodo-thyroxine and inorganic iodine produced effects on the form of the curve similar to those of thyroxine, but higher concentrations of these substances were necessary.