In the case of the thyroid the function of the gland appears to be to prepare a secretion which is poured out into the blood and alters tissue-change.
The thyroid gland, which is situated in front of the neck, yields a secretion which passes into the blood and there tends to maintain a state of moderate dilatation in the blood-vessels and of oxidization in the tissues, so that the circulation remains good and the body-heat and muscular activity remain well maintained.
One point must not be omitted, namely, the homogeny of the endostyle of Amphioxus and the thyroid gland of Craniata.
When the thyroid tablets or extract of thyroid are given in too large quantities to patients suffering from myxoedema, the symptoms of myxoedema disappear, but in their place appear others indicative of increased metabolism and accelerated circulation.
The larynx has the lateral sacculi well developed, though entirely concealed within the alae of the thyroid cartilage.
In the normal thyroid there is formed and stored up in the spaces this colloid material.
Hippocrates had no opportunity of verification by necropsy, and Sydenham ignored pathology; yet the clinical features of many but recently described diseases, such, for example, as that named after Graves, and myxoedema, both associated with perversions of the thyroid gland, lay as open to the eye of physicians in the past as to our own.
The whole of the secretion here is poured into the blood and not at all on to a mucous surface, and herein the thyroid gland differs largely from such glands as the pancreas or peptic and intestinal glands.
When the thyroid is hypertrophied, as in Graves's disease, the same symptoms are observed, and these are probably due to increased secretion from the thyroid.
Observations were made on the connexion between thyroid gland and myxoedema, which appeared to show that this disease was dependent upon atrophy of the gland.