VASCULAR OR DUCTLESS GLANDS. 145 



thyroid itself; viz., a diminution of all myxedematous symptoms. In normal 

 states of the body, thyroiodin influences very actively the general metabolism. 

 It gives rise to a decomposition of fats and proteins and to a decline in body- 

 weight. In large doses it may produce toxic symptoms: e. g., increased 

 cardiac action, vertigo, and glycosuria. 



The conclusions as to the functions of the thyroid gland which have 

 been drawn from the results that have followed its removal from animals 

 by surgical procedures, have been made questionable, since the discovery 

 of the parathyroid glands and a study of the phenomena which follow when 

 they alone are removed. From their situation and close relationship to the 

 thyroid gland it is generally accepted, that in the earlier experiments, espe- 

 cially those made on cats and dogs, and some other carnivorous animals, both 

 sets of glands were removed and hence some of the symptoms which developed 

 after the removal of the thyroids were due to the loss of function not of the 

 thyroid but of the parathyroids. 



The fibrillar contractions, the tremors and spasms are due to parathyroid 

 removal; the myxedema and the failure of the mental powers, to the re- 

 moval of the thyroid. 



The Parathyroids. The parathyroids are small bodies, usually four 

 in number, two on each side. They are divided into superior and inferior. 

 The superior are situated internally and on the posterior surface in close 

 relation to, and frequently imbedded in, the substance of the thyroid; the 

 inferior are situated externally, sometimes in contact with, and at other times 

 removed a variable distance from the thyroid. Microscopically the para- 

 thyroids consist of thick cords of epithelial cells separated by septa of fine 

 connective tissue and surrounded by capillary blood-vessels. Chemic 

 analysis shows that they also contain iodin in combination with some organic 

 compound. 



Effects of Parathyroid Removal. The surgical removal of the para- 

 thyroids is followed in the course of from two to five days by the death of the 

 animal preceded in most instances by a series of symptoms which are em- 

 braced under the general term "tetany." These symptoms are fibrillary 

 contractions of muscles, tremors, spasmodic contractions and paralyses 

 of groups of muscles and not infrequently convulsive seizures and coma. 

 During the convulsion there is an acceleration of the heart-beat, and increase 

 in the respiratory movements which frequently become dyspneic in character. 

 There is also a loss of appetite, nausea, mucous vomiting, and diarrhea. 

 Death may occur during a convulsion or from coma. (Morat and Doyon.) 



These results for the most part occur only when ail the parathyroids 

 are removed. It is asserted that even if one gland is retained the animal 

 TO 



