THE THYKOli) GLAND AND ITS DISEASES 231 



Asher and Flack (6) utilized, the observation of V. Cyon that the ex- 

 citability of the depressor nerve is increased by the action of thyroid sub- 

 stance. They believe that the thyroid furnishes an internal secretion which 

 increases the excitability of the depressor nerve, and augments the effect 

 of epinephrin upon the blood-pressure. According to these authors the 

 secretory nerves to the gland are the laryngeal nerves. 



More recent investigation seems to point to the sympathetic as the 

 origin of the secretory nerves to the thyroid. Rahe, Rogers, Fawcett and 

 Beebe find that stimulation of vessels with the accompanying nerve fila- 

 ments causes a diminution in the amount of iodin contained in the gland. 

 These authors conclude that the thyroid is at least in part under nervous 

 control, and that its physiologically active substance is discharged into the 

 circulation in response to a nerve stimulus. 



The view that the sympathetic fibers are true secretory nerves to the 

 thyroid is supported by the observations of Cannon and Cattell upon the 

 electrical response of the gland during activity. Control by the sympa- 

 thetic suggests that adrenin may stimulate the thyroid to increased ac- 

 tivity, and this was proved to be the case by intravenous injection of 

 adrenin, and by stimulation of the adrenals through the autonomic nerves. 

 By continuous stimulation (fusion with the phrenic) of the cervical sym- 

 pathetic a condition resembling exophthalmic goiter was produced. It 

 seems possible that the thyroid (like the suprarenal) has an emergency 

 function, which would increase the rate of metabolism and augment the 

 efficiency of the adrenin secreted simultaneously (Cannon and Fitz). 



Rogoff tried to detect in the blood coming from the thyroids of three 

 dogs a physiologically active secretion, tested by feeding tadpoles with the 

 dried blood. Only one dog gave evidence of an active pouring out of 

 thyroid secretion into the blood. In this case the blood was collected 

 from the glands during massage and stimulation of the cervical sympa- 

 thetic nerve. The number of experiments here recorded is not sufficient 

 to warrant us in drawing any very definite conclusion. 



The Nature of the Substance Secreted by the Thyroid and Its Physio- 

 logical Actions. A detailed consideration of the nature and actions of 

 the various thyroid derivatives will be found in the chapter on "Chemistry 

 of the Thyroid." Merely a few of the outstanding features will be 

 mentioned here. 



In 1895 Baumann (.) discovered the presence of iodin in the thyroid 

 gland, and prepared a substance from it containing 9.3 per cent of iodin. 

 The substance is known as "thyroidin." 



Oswald (&) (e) in 1899 considered the iodin of the thyroid gland to be 

 bound up in a globulin-like body, and the compound was called by him 

 "thyreoglobulin." 



Neither of these substances appears to. have been chemically pure. More 

 recently Kendall (c) (i) has isolated a white crystalline substance from 



