THE ADRENAL GLANDS 747 



splanchnic nerve before it reaches the adrenal gland. This last result, 

 which is the most important in the present connection, was, however, not 

 observed when the blood of the inferior vena cava was prevented by the 

 application of a clamp from getting to the heart, but immediately ap- 

 peared, after stimulation, when the clamp was removed. This experiment 

 taken alone does not, however, justify the conclusion that there is any 

 direct relationship between the adrenal glands and the thyroid, because 

 there are in the thyroid gland structures such as the muscle fibers in the 

 blood vessels, which a hypersecretion of epinephrine might affect. Before 

 any direct relationship between the two glands could be claimed to exist, 

 it would be necessary to show that the thyroid action current is obtained 

 with a concentration of epinephrine in the blood lower than that affecting 

 the blood vessels. 



2. With the Sexual Glajids. As mentioned above, a very direct rela- 

 tionship exists between the development of the sexual glands and that of 

 the suprarenals, particularly the cortex of the glands. In addition to the 

 evidence above furnished, it may be mentioned that in hyperplasia of the 

 adrenals changes occur in the testicles, particularly in their interstitial 

 cells. 



3. With the Liver. Of the many functions of this gland that which is 

 most directly associated with epinephrine is the production of glucose 

 from glycogen the glycogenolytic process (see page 669). The injection 

 of epinephrine causes an immediate discharge of such an excess of glucose 

 into the blood that hyperglycemia and glycosuria immediately follow. 

 This result is most striking when the injection is made in glycogen-rich 

 animals. In animals from which all the glycogen of the liver has been 

 removed by starvation, the injection of large amounts of epinephrine 

 causes glycogen to accumulate in the liver cells a result which it is 

 difficult to interpret. 



In the light of the fact that stimulation of the great splanchnic nerve 

 causes a demonstrable increase of epinephrine in the blood, a natural con- 

 clusion is that the glycosuria and hyperglycemia which are known to re- 

 sult from stimulation of the splanchnic nerve or of its center in the 

 medulla, must be dependent upon a hypersecretion of epinephrine. 

 Evidence supporting this hypothesis seemed to be furnished by the obser- 

 vation that, after the removal of the adrenal glands, stimulation of the 

 splanchnic or of the so-called "diabetic" center in the fourth ventricle 

 no longer produced glycosuria even in a glycogen-rich animal. But it is 

 difficult to see how such an important physiological process as that of the 

 nerve control of the production of sugar by the liver should be dependent 

 on the hypersecretion of the adrenal gland, especially since the epineph- 

 rine would have to be carried by the blood around a considerable part of 



