CHEMICAL REGULATION OF METABOLISM 387 



of the abnormality in drinking-water which causes disorders of the 

 thyroid. It cannot even be definitely stated whether the abnormality 

 consists in the presence of an infecting agent, or in a chemical compon- 

 ent or its absence. The numerous circumscribed and yet widely sepa- 

 rated areas of endemic occurrence, however, speak against the view 

 that the disease is communicated by an infecting organism. The goiter 

 which occurs among fishes in hatcheries, has been traced to overfeeding 

 with a high protein diet. 



Lying just above the thyroid, or, in some animals, imbedded in 

 the thyroid tissue, are a variable number (two pairs in man) of small 

 glands, known collectively as the Parathyroids. Structurally they differ 

 essentially from the thyroid and evidently they also differ from the 

 thyroid very decisively in function, for their excision leads to quite a 

 different sequence of events from those which follow thyroidectomy. 

 The removal of the parathyroids, if complete, results in acute neuro- 

 muscular symptoms which are collectively designated Tetany, and 

 which resemble very closely a condition which not infrequently arises 

 spontaneously in young children. For a little time succeeding para- 

 thyroidectomy, no abnormalities appear, but within forty-eight hours 

 tremors are observed in the extremities, followed by involuntary con- 

 tractions of more and more muscles of the body until, finally, convul- 

 sions supervene, terminating after several days in death. The condi- 

 tion is completely relieved, according to W. G. Macallum, by the 

 administration of Calcium Salts, and for this reason it was thought 

 probable, for some time, that the special function of the parathyroids 

 consists in the regulation of the Calcium Metabolism. Many facts, 

 however, speak against this view. In the first place observers are not 

 agreed that the excision of the parathyroids leads to increased excre- 

 tion of calcium or a reduction of calcium in the blood and tissues, and 

 in the second place other disturbances of metabolism to which attention 

 has been directed in recent years offer a more probable origin of the 

 neuromuscular symptoms. The remedial effect of calcium salts is 

 regarded merely as an example of the general action of calcium in reduc- 

 ing the irritability of nerve fibers. On the other hand some disturbance 

 of the calcium metabolism unquestionably accompanies parathyroidec- 

 tomy, for it has been found by Erdheim that parathyroidectomy in 

 rats (probably not complete) leads to deficient dentine-formation in 

 the teeth of the operated animals, and Erdheim and Carrel have found 

 that callus-formation in injured bones is delayed by parathyroidectomy. 



The effect of parathyroidectomy upon the nitrogenous metabolism 

 is very marked. The output of Ammonia is much increased, and for 

 this reason Kendall and others have suggested that the parathyroids 

 control the transformation of ammonium carbonate into Urea, which 

 is the normal end-result of the deaminization of amino-acids, and occurs 

 primarily in the liver. There is a decided Alkalosis or increased alka- 

 linity of the blood in parathyroidectomy, and the symptoms may be 

 alleviated by the injection of acids. On the other hand it has not 



