THE DUCTLESS GLANDS 



95 



excite activity in other organs, except in a few cases 

 where they inhibit such activity. They have, therefore, 

 been named hormones, meaning to excite, and chalones 

 when they inhibit or prevent activity. 



Fig. 21. The thyroid gland. (Gray's Anatomy, after Spalteholz.) 



While no adequate explanation of the function of the 

 thyroid and parathyroids can be given, it seems clear 

 that the former forms a hormone which stimulates other 



