868 PHYSIOLOGY OF DIGESTION AND SECRETION. 



The parathyroids are, according to most authors, quite different 

 structures. Four of these bodies are usually described, two on each 

 side, and their positions vary somewhat in different animals or, 

 indeed, in different individuals.* In man the superior (or internal) 

 parathyroids are found upon the posterior surface of the thyroid, 

 at the level of the junction of its upper with its middle third. They 

 may be imbedded in the thyroid tissue. The inferior (or external) 

 parathyroids lie near the lower margin of the thyroid on its poster- 

 ior surface and in some cases lower down on the sides of the trachea. 

 The tissue has a structure quite different from that of the thy- 

 roids, being composed of solid masses or columns of epithelial 

 cells which are not arranged in vesicles and contain no colloid. 



Extirpation of the Thyroids and Parathyroids. In 1856 

 Schiff showed that extirpation of the thyroids (complete thyroi- 

 dectomy) in dogs is followed usually by \,he death of the animal in 

 one to four weeks. The animal exhibits certain characteristic symp- 

 toms, such as muscular tremors, which may pass into convulsions, 

 cachexia, emaciation, and a condition of apathy. This result was 

 confirmed by subsequent observers, but many exceptions were noted. 

 Great interest was shown in these results, because on the surgical 

 side reports were made showing that after complete removal of the 

 thyroids in cases of goiter evil consequences might ensue, either 

 acute convulsive attacks or chronic malnutrition. On the other 

 hand> it became known that atrophy of the thyroids in the young 

 is responsible for the condition of arrested growth and deficient 

 mental development designated as cretinism, and in the adult the 

 same cause gives rise to the peculiar disease of myxedema, character- 

 ized by distressing mental deterioration, an edematous condition 

 of the skin, loss of hair, etc. Schiff and others found that the evil 

 results of complete thyroidectomy in dogs might be obviated by 

 grafting pieces of the thyroid in the body, and this knowledge was 

 quickly applied to human beings in cases of myxedema and cretinism 

 with astonishingly successful results. Instead of grafting thyroid 

 tissue it was found, in fact, that injection of extracts under the 

 skin or better still simple feeding of thyroid material gave similar 

 favorable results: the individuals recovered their normal appear- 

 ance and mental powers. f It is stated that in cases of myxedema 

 the patient may be kept in perfect health by the administration of a 



* Thompson, "Philosophical Transactions, Roy. Soc.," London, B. 201, 

 91, 1910. 



f For a general account of the development of the subject and the liter- 

 ature see 'Transactions of the Congress of American Physicians and Sur- 

 geons" (Howell, Chittenden, Adami, Putnam, Kinnicutt, Osier), 1897; Jean- 

 delize, "Insuffisance thyroidienne et parathyroidienne," Nancy, 1902; Vincent, 

 "Internal Secretions," etc., Lancet, Aug. 11 and 18, 1906; also "Ergebnisse der 

 Physiologic," 11, 1911; Biedl, "Innere Sekretion," Berlin, 1913. 



