ADRENALS 637 



As in the case of other glands forming an internal secretion, it 

 has been debated whether the function of the thyroid is to destroy 

 toxic bodies or to form substances indispensable or advantageous 

 to the organism. While the precise role played by the organ in the 

 economy remains obscure, it is evident that in most animals and in 

 man its secretion is of great importance, whether it be solely the 

 quasi-external secretion of ' colloid/ containing the thyroiodin, that 

 collects in its alveoli and slowly passes out of them by the lym- 

 phatics, or perhaps, in addition, some other substance, which, like 

 the glycogen of the liver, never finds its way into the lumen of the 

 gland-tubes at all. It may also be admitted that, by aiding in the 

 maintenance of the normal level of general nutrition, particularly 

 that of the central nervous system, the ability of the organism to 

 cope with toxic substances introduced from the outside or manu- 

 factured in the body is favoured. There is, however, no evidence 

 that an actual destruction or neutralization of toxic substances 

 occurs in the gland itself. 



fit is probable that the secretion of the thyroid is influenced by 

 nerves. Section of the superior and inferior thyroid nerves going 

 to the gland is followed by degenerative changes in it. J It has been 

 stated that stimulation in the dog of the nerves entering one thyroid 

 lobe on the bloodvessels, or of the cephalic end of the vago-sympa- 

 thetic nerve below the superior cervical ganglion, causes a diminu- 

 tion in the iodine content of that lobe as compared with the other 

 (Fawcett and Beebe). This result has been interpreted as due to the 

 excitation of fibres which accelerate the passage of the active 

 substance out of the gland. It has long been known that vaso- 

 motor fibres for the dog's thyroid run up in the cervical sympathetic 

 to the superior cervical ganglion, and thence to the lobe of the 

 same side. These were first discovered by the effect produced by 

 their stimulation on the thyroid circulation time (p. 135). Further 

 evidence of the existence of secretory fibres has been brought for- 

 ward by Asher and Flack. They compared the excitability of the 

 depressor nerve, and also the effect on the blood-pressure of the 

 intravenous injection of adrenalin, before and during stimulation 

 of the thyroid nerves. They conclude that, when all the other 

 conditions remain unchanged, both the effect of excitation of the 

 depressor and the effect of adrenalin are greater during stimulation 

 of the thyroid nerves than shortly before it without such stimula- 

 tion. The difference is really connected with the internal secretion 

 of the thyroid, since it is not obtained if the thyroids are previously 

 extirpated, and injection of thyroid extracts influences the result 

 exactly in the same way as stimulation of the thyroid nerves. 

 (Adrenal Bodies, j-ftt had been observed by Addison that the 

 malady which now Dears his name, and in which certain vascular 

 changes, with muscular weakness, anosmia, and pigmentation or 



