Prothoracicotropic hormone
Prothoracicotropic hormone (PTTH) was the first insect hormone to be discovered. It was originally described simply as "brain hormone" by early workers such as Stefan Kopeć (1922) and Vincent Wigglesworth (1934), who realized that ligation of the head of immature insects could prevent molting or pupation of the body region excluded from the head if the ligation was performed before a critical age in the lifestage was reached. After a certain point the ligation had no effect and both sections of the insect would molt or pupate. However, implantation of a conspecific brain to a sessile ligated abdomen or an abdomen under diapause would induce molting or pupation. Thus, the brain was originally thought to be the source of the hormone that induces molting in insects.
Ray Farquharson
Through his research in endocrinology with colleague Arthur Squires, Farquharson discovered what became known as the "Farquharson Phenomenon": that the introduction of continuous exogenous hormone doses suppresses the natural production of that hormone in the patient and causes temporary atrophy in the producing organ. This phenomenon became one of the basic principles of endocrinology and a key factor in the etiology of hormonal abnormalities. Farquharson also made significant contributions related to anemia and pigment metabolism. He was the first Canadian doctor to publicize Sheehan's syndrome, and the first North American to report on Simmond's disease. As an educator and researcher, he was an early promoter of laboratory testing in the evaluation of illness; he was known for advocating both this and awareness of potential psychological issues in patients.