3
of various sizes lined by cubical epithelial cells and surrounded by connective tissue in which lie lymph spaces and blood vessels. The central part of each alveolus is filled by the colloid substance which is secreted by the epithelial cells. This secretion escapes into the lymphatic spaces, either in consequence of rupture of the wall of the alveolus or by minute channels which pass between the epithelial cells. From the lymph spaces it passes into the blood by the lymphatic vessels. The general appearance of the gland is shown in Fig. 1. Now compare this with the appearance presented by the thyroid gland of a patient suffering from myxœdema, for which I am indebted to Dr. Callcott of Gosforth. Here we see an advanced stage of fibrosis of the gland. Only three alveoli are left in the portion represented in Fig. 2, and even in them the epithelial cells have to a considerable extent
Fig 1.—Normal thyroid gland. Drawn through Zeiss obj. D. Oc. 2, with camera lucida.
either undergone partial degeneration or disappeared altogether. All the rest of the field is occupied by dense fibrous tissue and masses of small round cells. It is obvious that this gland must have been nearly functionless.
As an illustration of the changes which take place in the thyroid gland when a part of it undergoes hypertrophy so as to respond to the demand for increased secretory activity caused by the removal of the rest of the gland, we may take the following experiment[1]:—On January 5th, 1894, the thyroid gland was removed from a Rhœsus monkey while under the influence of ether. Subsequent events proved that a piece of the gland was accidentally left behind, so that instead of a complete thyroidectomy only a partial one was in reality performed.
- ↑ The expenses of this experiment were partly defrayed by a grant from the Scientific Grants Committee of the British Medical Association.
