Researchers First Discovered the Existence of Hormones by Studying Secretions

Question

Researchers first discovered the existence of hormones by studying secretions from the ________.  
A) adrenal glands
B) pancreas
C) gonads
D) thymus gland
E) pineal gland

Accepted Answer

Researchers first discovered the existence of hormones by studying secretions from the pancreas, specifically through the work on insulin.