Chap. 15 



CHEMICAL REGULATION ENDOCRINE GLANDS 



261 



Fig. 15.5. Sections of active thyroid glands of the salamander (Triturus viri- 

 descens). Thyroid glands are composed of vesicles or follicles lined by a single 

 layer of secretory cells. The cavities of the follicles contain the hormone produced 

 by those cells. This is absorbed into the blood through the walls of the blood 

 vessels between the follicles where there is connective tissue, fat and nerve cells. 

 Left, Section of a whole gland under low power. It is about half the size of an 

 apple seed. The white tips of the secretory cells are bulging with secretion. The 

 nuclei appear black. Right, Section of a gland under high power. The white tips 

 of cells full of thyroid secretion project into that which (dark) is stored ready to 

 be absorbed by the blood. 



Goiter. It is an enlargement of the thyroid gland. There may be too little 

 secretion; in hypothyroid goiter the cells increase in order to bring the secre- 

 tion to a normal amount; in hyperthyroid goiter the gland secretes an excess 

 usually with a great multiplication of cells. Either of these conditions may 

 occur without an enlargement of the gland. 



The association of the thyroid and goiter has long been known. Nearly 

 2,000 years ago, Juvenal, a Roman poet, remarked on the prevalence of goiter 

 in the Alps. In the 16th century the Swiss physician, Paracelsus, wrote of the 

 seriousness of goiter near the famous music center of Salzburg, and agreed 

 with others that the cases were caused by the mineral content of the drinking 

 water. Long before this, about 1180, another physician, Roger of Palermo, 

 had found a remedy for goiter in the ashes of sponges and seaweed. In 1910, 

 David Marine, a physician in a New York hospital, made a study of the goiter 

 occurring in hundreds of brook trout at a hatchery in the mountains of Penn- 

 sylvania. He placed small amounts of iodine in the runways, mixed iodine with 

 their food, and, like Roger of Palermo, included seafoods in their rations 

 (Fig. 15.4). A general recovery soon spread through the population. Follow- 

 ing this experiment human subjects were similarly treated in a region of Ohio 

 where goiter was prevalent, and again the goiter disappeared. The localities 

 peculiar to this commonest disease of the thyroid, all of them far from the sea, 



