THE ADRENAL GLANDS 129 



ate the neck and sometimes so compress the trachea as to inter- 

 fere with breathing. The cases of chronic goitre occur in the 

 same districts in which the exophthalmic variety is common, these 

 being, in this country, the shores of the great inland lakes and 

 the river valleys, but not in districts bordering on the sea. They 

 are also common in certain districts in Switzerland and Eng- 

 land. It is of interest that in the lake and river districts in 

 this country the thyroids of over ninety per cent of all dogs are 

 more or less hypertrophied. 



The above remarkable influence of the thyroids on metabolism 

 is in some way dependent upon the colloid material which fills 

 the vesicles. This colloid contains a peculiar substance called 

 iodothyrin, because it contains iodine, an element which is not 

 found present in any other part of the animal body. 



The Adrenal Glands. As their name signifies, these are situ- 

 ated one on either side just above the kidneys. Each gland is 

 yellowish in color, and is seen on microscopic examination to be 

 composed of a medullary and a cortical portion. The medulla 

 consists of irregular collections of cells containing granules 

 which stain deeply brown with chronic acid and are therefore 

 called chromophile granules. Similar chromophile granules may 

 exist in other parts of the body. The great splanchnic nerve, 

 which it will be remembered arises from the sympathetic chain 

 in the thorax (see p. 278), makes very intimate connection with 

 the adrenal medulla, for which reason and because of the fact 

 that it is developed from the same embryonic tissue as the sym- 

 pathetic system of nerves, the medulla of the adrenal gland is 

 believed to be closely bound up with the functions of the sympa- 

 thetic nervous system. The cortex is composed of rows of col- 

 umnar cells which do not contain chromophile granules. Small 

 though they be, the adrenal glands are essential to life, for their 

 removal causes extreme muscular weakness and a fall in blood 

 pressure followed by death within twenty-four hours. When 

 they are the seat of disease (tubercular), symptoms of extreme 

 muscular prostration, accompanied by vomiting and a peculiar 

 bronzing of the skin, set in and grow steadily worse until at last 

 the patient succumbs. This is called Addison's disease. 



