596 



VETERINARY PHYSIOLOGY 



2. Structure — It early loses its connection with the ali- 

 mentary canal, and becomes cut up by fibrous tissue into a 

 number of small more or less rounded cysts or follicles, each 

 lined with cubical epithelium and filled with a mucus-like 

 colloid substance, with a marked affinity for acid stains 

 (fig. 229). It is enormously vascular and has a rich supply 

 of lymphatics. 



3. Chemistry — The colloid substance is characterised by 

 containing iodine, but the amount varies in different animals 

 and in the same animal according to the mode of feeding. 





Fig. 229. — Section through Part of the Thyreoid (Th.) and a Parathyreoid (P.) 



of a Mammal. 



A very stable organic compound of iodine, known as iodothyrin, 

 may be prepared, but this is actually combined in a globulin- 

 compound which is the active constituent of the organ, and is 

 known as iodothyreoglobulin. Kendall has described a crystal- 

 line product of definite composition containing the indol nucleus 

 (p. 330) with iodine attached to the benzene ring — a thyreo- 

 oxyindol- 



4. Physiology. — In 1873 Gull described a peculiar disease 

 chiefly affecting women which has received the name of myx- 

 cedema (p. 597), and in 1877 Ord was able to show that it is 

 associated with atrophy of the thyreoid. Kocher and the 



