308 THE DUCTLESS GLANDS 



depressor nerve, and augments the effect of adrenin 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 fibres to the thyroid. Rahe, 

 Rogers, Fawcett, and Beebe find that stimulation of vessels with 

 the accompanying nerve filaments causes a diminution in the 

 amount of iodin contained in the gland. These authors con- 

 clude 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 fibres 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. (See p. 33.) Control by the sympathetic suggests that 

 adrenin may stimulate the thyroid to increased activity, and 

 this was proved to be the case by intravenous injection of 

 adrenin, and by stimulation of the adrenals through the 

 sympathetic nerves. By continuous stimulation (fusion with 

 the phrenic) of the cervical sympathetic a condition resembling 

 exophthalmic goitre was produced. It seems possible that the 

 thyroid (like the adrenal) has an emergency function, which 

 would increase the rate of metabolism and augment the 

 efficiency of the adrenin secreted simultaneously. 



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. The number of 

 experiments recorded is not sufficient to warrant us in 

 drawing any very definite conclusion. 



M. The Chemistry of the Thyroid 



The most striking feature of the thyroid gland from a 

 chemical standpoint is the constant presence in it, under 

 normal conditions, of measurable amounts of iodine. 



The following elements have been stated to be present in 

 the thyroid : carbon, hydrogen, oxygen, nitrogen, sulphur, 

 phosphorus, sodium, potassium, calcium, magnesium, silicon, 

 arsenic, fluorine, chlorine, bromine, and iodine. It was in 

 1854 that Macadam found iodine in food plants, but it was 

 not until 1895 that Baumann discovered the presence of this 



