THE THYKOID GLAND AND ITS DISEASES 491 



have described increased metabolism in some cases of pernicious anemia. 

 These exceptions are difficult to explain. 



The Hyperjjlycemia Test 



Relation of the Thyroid to Carbohydrate Metabolism. Thyroid se- 

 cretion plays a very important role in the carbohydrate metabolism of the 

 body. Thus, it has been shown by King that the thyroid gland exerts 

 a retarding action on the carbohydrate-destroying mechanism of the body 

 as does also the active constituent of the gland, "iodothyrin," even in a 

 more marked way. This action of the thyroid is quite independent of 

 any relationship with other endocrin glands or with the nervous system. 

 It would seem that the thyroid inhibits the direct combustion of sugar 

 in the muscles, probably by inhibiting the action of the pancreatic and 

 muscle ferments which cause the actual oxidation of dextrose. Further- 

 more, it has been shown by Kuriyama that thyroid feeding to white rats 

 produces a decreased glycogen content of the liver. He did not find, 

 however, that experimental hyperthyroidism produces any change in the 

 sugar content of the blood in either rats or rabbits. 



Other hypotheses have been advanced to explain the production of 

 hyperglycemia in hyperthyroidism. Some believe that the thyroid secre- 

 tion acts on the suprarenal glands stimulating them to increased activity, 

 or that the thyroid hormone acts on some other of the endocrin glands 

 concerned in sugar metabolism. Allen believes that the hyperglycemia is 

 produced by the action of the thyroid on the nervous system. It is as a 

 result of these influences, doubtless, that increased amounts of blood 

 sugar have been found in hyperthyroidism and in extreme cases occa- 

 sional glycosuria. The determination of this increased sugar content of 

 the blood has led to the confirmatory hyperglycemia test. 



Carbohydrate Tolerance in Experimental and Clinical 



Hyperthyroidism 



The sugar content of the blood does not change in experimental 

 hyperthyroidism (Kuriyama) nor does spontaneous glycosuria result from 

 thyroid feeding in either rats or rabbits. The tolerance for dextrose 

 parenterally administered to thyroid-fed rabbits does not differ from that 

 of normal animals (Kuriyama). Turning now to clinical hyperthyroid- 

 ism, we find that spontaneous glycosuria has long been known to occur 

 in exophthalmic goiter (Kraus and Ludwig, Chvostek, von Noorden (&), 

 Garrod (a)). This is doubtless due to the fact that the normal use of 

 carbohydrates is made more difficult by the increased amounts- of thyroid 



