580 INTERNAL SECRETION 



alkalies. It contains phosphorus and about 10 per cent, of iodine, 

 but it gives no proteid reactions. 



The effects produced by iodothyrin are similar to those caused 

 by extracts of the whole gland. Patients suffering from cretinism 

 or myxcedema are greatly improved by this method of treatment. 

 The abnormal conditions disappear ; the metabolism, which in 

 these diseases is abnormally low, is raised to the level of health ; 

 the absorption and assimilation of food and the secretion of urine 

 are increased. It is interesting to note that toxic symptoms have 

 been observed after the administration of large doses of thyroid 

 extract to men and animals not suffering from disease or removal 

 of the gland. Cardiac weakness, wasting, and the discharge of 

 albumin and sugar in the urine may be produced. The intravenous 

 injection of thyroid extract produces a fall of blood-pressure, but 

 this may not be a specific effect. 



The foregoing data show the great importance of the thyroid 

 gland for the maintenance of the healthy metabolism of the body, 

 but they do not show how it acts. Upon this latter point there 

 are two chief theories. The more probable one is that the gland 

 produces a specific substance which is necessary for the nutrition 

 of the body, especially of the central nervous system ; not only 

 do the symptoms during life show that that system is especially 

 affected by the loss of the thyroid, but after death degenerative 

 changes are found in the nerve -cells of the brain and spinal cord. 

 The rival theory maintains that the thyroid gland produces a 

 substance which neutralises or antagonises poisonous products 

 produced by the metabolism of the body. Our present knowledge, 

 however, of the chemical changes which occur in the living body is so 

 incomplete that it is impossible to dogmatise upon this question. 



So far nothing has been said about the Parathyroid Glands, 

 small glands which lie on each side of the neck, and often in close 

 relationship to, or even embedded in, the thyroid gland. In 

 minute structure they do not resemble the thyroid gland, for they 

 consist of cells arranged more or less in columns and contain no 

 vesicles and no colloid. The parathyroids were described by 

 Sandstroem in 1880 as embryonic remnants of the thyroid gland ; 

 their functions were first investigated by Gley a few years later. 

 Since that time numerous experiments have been made by various 

 observers, and a different view has arisen as to the functions of 

 the thyroid and parathyroid glands. It is maintained that re- 



