The brain-cells and the adrenals are securely, concealed from the eye of the clinician, hence the changes produced in them by different causes escape his notice, but the thyroid has always been closely scrutinized by him. The clinician knows that every one of the above-mentioned causes of increased brain-cell, adrenal, liver and muscle activity may cause an increase in the activity of both the normal or the enlarged thyroid; and lie knows only too well that in a given case of exophthalmic goiter the same stimuli which excite the brain, the adrenals, the liver, and the muscles to increased activity will also aggravate this disease. The function of the thyroid in the kinetic chain is best evidenced, however, by its role in the production of fever. Fever results from the administration of thyroid extract alone in large doses. In the hyperactivity of the thyroid in exophthalmic goiter one sees a marked tendency to fever, in severe cases there is daily fever. In fact, in Graves' disease we find displayed to an extraordinary degree an exaggeration of the whole action of the kinetic mechanism. We have stated that in acute Graves' disease there is a tendency to the production of spontaneous fever, and that there is a magnified diurnal variation in temperature which is due to an increased output of energy in even the normal reaction producing consciousness. In Graves' disease there is, therefore, a state of intensified consciousness, which is associated with low brain thresholds to all stimuli--both to stimuli that cause muscular action and to stimuli that cause fever. The intensity of the kinetic discharge is seen in the constant fine tremor. It is evident that the thresholds of the brain have been sensitized. In this hypersensitization we find the following strong evidence as to the identity of the various mechanisms for the production of fever. In the state of superlative sensitization which is seen in Graves' disease we find that the stimuli that produce muscular movement, the stimuli that produce emotional phenomena, and the stimuli that produce fever are as nearly as can be ascertained equally effective. Clinical evidence regarding this point is abundant, for in patients with Graves' disease we find that the three types of conversion of energy resulting from emotional stimulation, from infection stimulation, and from nociceptor stimulation (pain), are, as nearly as can be judged, equally exaggerated. In the acute cases of Graves' disease the explosive conversion of latent energy into heat and motion is unexcelled by any other known normal or pathologic phenomenon. Excessive thyroid secretion, as in thyrotoxicosis from functioning adenomata, and excessive thyroid feeding, cause all the phenomena of Graves' disease except the exophthalmos and the emotional facies (Figs. 15 and 23). The ligation of arteries, the division of its nerve supply, or the excision of part of the gland, may reverse the foregoing picture