THE RELATIONS BETWEEN THE ENDOCRIN ORGANS 171 



The Thyroid Gland 



The interrelationship between the vegetative nerves and the thyroid 

 gland on the one hand, and the secretion of the thyroid and the vegetative 

 nerves on the other, is not as clear and definite as that between these 

 nerves and the suprarenals. 



Control of Thyroid Secretion. Cannon and his coworkers (1916) 

 have done much to clarify the relationship of the vegetative nerves to the 

 gland. After satisfying themselves that certain electrical reactions are 

 due alone to secreting processes, they proceeded to investigate the thy- 

 roid, and show by the development of an action current that the sympa- 

 thetic nerves which are distributed to it supply its secretory fibers. Stimu- 

 lation of the vagus fibers to the thyroid, on the other hand, failed to cause 

 any action current in the gland ; hence it was concluded that these fibers 

 have no control on the secretory processes, as has been claimed by Asher 

 and his coworkers. To further test this experimental result, they first in- 

 jected epinephrin (one^tenth to one-fifth of a 1 :100,000 dilution) in a cat 

 and produced the electrical reaction indicative of secretory activity. Then 

 the splanchnic nerves to the suprarenals which had previously been sepa- 

 rated from their connection with the central nervous system were stimu- 

 lated to bring about discharge of epinephrin. Again an action current 

 was detected in the thyroid. These experiments seem to show definitely 

 that the sympathetic fibers are the secretory nerves of the thyroid, and 

 further, to establish the basis for the accepted fact of the close relationship 

 between the secretion of the suprarenals and the thyroid. 



Clinical Significance of the Thyroid-Sympathetic Relationship. Clin- 

 ically this close relationship is sometimes evident and sometimes not, the 

 reason for which must be plain to any one who appreciates the complexity 

 of clinical reactions. One can, when working experimentally, apply a 

 stimulus definitely to a given organ or structure. Under clinical condi- 

 tions, however, a given stimulus is frequently not directed to a single 

 organ or tissue, but expends itself upon the organism as a whole, produc- 

 ing widespread reactions. A multiplicity of such stimuli may produce 

 complex syndromes. 



The effect of the major emotions in stimulating the sympathetics, as 

 shown by Cannon (1915), lays an experimental basis for the observation 

 made by clinicians that conditions of hyperthyroidism often follow emo- 

 tional excitement, a point which has been particularly emphasized by 

 Crile. The same ground for a hypersecretion exists in cases of toxemia; 

 for toxemia expresses itself peripherally through the sympathetics. In 

 this way we can see how such conditions as tuberculosis (Pottenger) (a-) 

 , syphilis, and intestinal toxemia (McCarrison), and infections 



