PARATHYROID GLANDS 77 



There is abundant evidence that iodides, and 

 especially organic combinations of iodine such as 

 iodoform, have great power in enhancing the 

 activity of the thyroid gland. We have already 

 seen that the gland normally secretes iodine into the 

 blood-stream, combined with a globuhn. Roos, 

 and more recently Hunt and Seidel, have shown 

 that the activity of the colloid varies directly with 

 the amount of iodine contained in it. When iodides 

 or iodoform are given by mouth, they are taken up 

 by the thyroid and secreted in the blood-stream in 

 the form of iodothyrin, the normal active principle 

 of the gland. The amount of iodine in the gland in 

 these circumstances rises considerably, as has been 

 proved by Oswald in man, and by Hunt and Seidel 

 in dogs. 



What, then, is the relation between iodine 

 metabolism and goitre ? 



In the first place, we may conclude that the 

 thyroid enlarges in goitre because it is necessary 

 for it to do increased work. A certain quantity of 

 iodothyrin is needful for the general well-being of the 

 individual ; if the gland is scantily suppUed with 

 iodine, it must enlarge in order to take the fullest 

 possible advantage of all that may be brought to 

 it by the blood-stream. In the same way a kidney 

 hypertrophies when its fellow is degenerated, in order 

 to obtain more urea for excretion ; and the red blood- 

 corpuscles double in number when a man takes up 

 his abode in the rarefied atmosphere of great alti- 

 tudes, to make the best use of the diminished supply 

 of oxygen. It has been shown by Oswald in a number 



