Abstract
1. Gentle massage of the thyroid gland in the cat for two or three minutes will cause an increased rate of the denervated heart amounting in some instances to 33 per cent. over the basal rate. The development of the maximal increase of rate is usually slow, requiring from thirty to sixty minutes and passing off in a similarly slow manner.
2. Massage of another gland, e.g., the submaxillary, does not cause this effect.
3. The augmentation of heart rate caused by thyroid massage occurs in the absence of the adrenal glands.
4. Stimulation of the cervical sympathetic trunk as it leaves the stellate ganglion induces a similar augmentation of the rate of the denervated heart: this does not occur if the thyroid gland has previously been removed.
5. If the cardiac fibers from the stellate ganglia are severed, as well as the vagus nerves, and an afferent nerve such as the sciatic or brachial is stimulated under a degree of anesthesia which will permit reflex retraction of the nictitating membrane and dilation of the pupil, there is a primary increase of rate due to adrenal secretion, followed by the slowly developing increase characteristic of the thyroid effect.
6. If the vagi and the cardiac fibers of the stellate are cut, and the animal is asphyxiated under conditions which permit the eye changes described above, there is a similar primary rise due to adrenal secretion, followed by the secondary thyroid effect.
7. If the thyroid glands have been previously removed, sensory stimulation and asphyxia induce only the increase of rate due to adrenal discharge.
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