SECRETION OF THE DUCTLESS GLANDS. 795 



tissue has a structure quite different from that of the thyroids, 

 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 the death of the animal in 

 one to four weeks. The aninial 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 chonic 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 edema tous condition 

 of the skin, loss of hair, etc. SchifT 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.* Later Baumannf succeeded in isolating 

 from the glands a substance designated as iodothyrin, which shows 

 in large measure the beneficial influence exerted by thyroid extracts 

 in cases of myxedema and parenchymatous goiter. This substance 

 is characterized by containing a large amount of iodin (9.3 per 

 cent, of the dry weight). It is contained in the gland in combina- 

 tion with protein bodies, from which it may be separated by diges- 

 tion with gastric juice or by boiling with acids. 



The Function of the Parathyroids. Most of the results des- 

 cribed above were obtained before the existence of the parathy- 

 roids was recognized. Early in the history of the subject it was 

 recognized that complete removal of the thyroids proper in herbiv- 

 orous animals (rats, rabbits) is not attended by a fatal result. 

 Gley and others, however, proved that if the parathyroids also are 



* 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, and 

 Jeandelize, 'Insuffisance thyroidienne et parathyroidienne, " Nancy, 1902 ; 

 also Vincent, 'Internal Secretions," etc., Lancet, Aug. 11 and 18, 1906. 



fZeitschrift f. physiolog. Chemie," 21, 319, and 481, 1896. 



