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PHYSIOLOGY: IV. B. CANNON 
causes a diminished iodine content of the gland. Severance of the 
vagus nerve supply has no effect. 
If the thyroid gland and neighboring indifferent tissue are connected 
through a galvanometer, stimulation of the sympathetic strand high 
in the thorax evokes an action current after a latent period varying 
usually between 5 and 7 seconds. This effect persists after the superior 
and the recurrent laryngeal nerves are severed. Experiments have 
shown that the nerve impulses pass out through both the superior and 
inferior cervical ganglia. 
Simulation of the main trunk of the vagus nerve in a curarized ani- 
mal, or injection of pilocarpine (which excites vagus endings) has no 
effect in producing an action current in the thyroid gland. 
The influence of sympathetic impulses is not indirect through local 
anemia of the gland, for when the blood supply is wholly stopped by 
clamping the blood vessels for a period equal to that of sympathetic 
stimulation, no noteworthy electrical change is produced. 
The conclusion is drawn, therefore, that the nerves distributed to 
the thyroid cells belong to the sympathetic and not to the vagus sup- 
ply, and that their effects are not indirect through alterations of blood 
flow, indeed that they are true secretory nerves. 
It is known that the internal secretion of the adrenal gland, or adrenin, 
will have the same effect in the body as sympathetic nerve impulses. 
Injection of a small dose of adrenin, 0.1 to 0.2 cc. (1 :100,000), evokes a 
marked action current in the thyroid gland. Also, stimulation of the 
nerve to the adrenal gland so as to cause its secretion to be poured into 
the blood stream, will evoke a characteristic electrical change in the thy- 
roid. This electrical change does not occur if the return of blood from 
the abdomen is prevented, but takes place promptly when the pent 
blood is released. Furthermore, it fails to appear after stimulating 
these nerves if the adrenal glands have been previously removed. There 
is thus definitely established an influence of adrenal secretion on thyroid 
activity. 
Previous studies have shown that the adrenal glands are roused to 
special activity in times of emotional stress. The thyroid gland is sub- 
ject to the division of the nervous system which is brought into action 
in emotional excitement and which causes adrenal secretion. It is 
probable, therefore, that the thyroid, like the adrenal, has normally 
functions which are performed in times of critical emergency. It may 
be that such an emergency function is an exaggerated form of the routine 
activity of the gland. 
The complete account of these researches will be published in the 
American Journal of Physiology, July, 1916. 
