PHYSIOLOGY OF TO-DAY 



of these glands vary somewhat in different animals. In the 

 dog, which has served for most experimental work, there 

 is a stiffness of the muscles, associated with fibrillary 

 contractions or tremors, and later cramp-like and clonic 

 contractions, with eventually convulsive fits. Since death 

 always results after complete extirpation of all parathyroid 

 tissue in untreated animals, it is obvious that these small 

 structures are essential for life. 



The function of these glands remained obscure for a 

 long time. About twenty years ago, it was found that after 

 a removal of the parathyroid glands in dogs, the calcium 

 content of the blood was greatly reduced in amount. 

 This naturally led to an attempt to restore the calcium of 

 the body to normal artificially, by injection of a calcium 

 salt; and it was found that this treatment would relieve 

 the condition of tetany and restore the animal to normal 

 for a short period of time. The whole train of symptoms 

 of tetany was held to be due to a lowered calcium content 

 of the blood, which is normally controlled by the para- 

 thyroid glands. 



The above theory of the relationship of the parathyroids 

 to calcium metabolism did not, however, go unchallenged. 

 Another theory gained considerable vogue for a while; 

 namely, that the parathyroids act in the body as detoxi- 

 fying agents and that the symptoms after their removal 

 are due to the accumulation of toxic products normally 

 rendered innocuous by them. Indeed, certain substances, 

 called guanidine and methyl guanidine, were stated to 

 occur in the blood of parathyroidectomized animals in 

 abnormally large amounts. 



The proof that the parathyroid glands perform their 

 function by the production of a hormone which is inti- 

 mately related to the metabolism of calcium has come 

 only in the last few years. This proof consists in the ex- 

 traction of the hormone from the glands of cattle — in a 



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