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.
Herbert McLean Evans
His medical research at Berkeley addressed problems relating to human nutrition, endocrinology, embryology, and histology. In 1918, his research into the number of human chromosomes led him to believe the number to be 48, when most people assumed the number to be much higher. It was only later discovered that the correct figure was 46. Evans had much greater success however with hormones extracted from the anterior lobe of the pituitary gland. He isolated Human Growth Hormone, which is essential for human growth and development. In 1922 along with Katharine Scott Bishop, during feeding experiments on rats, he co-discovered Vitamin E which is needed for human reproduction. Evans became director of the Institute of Experimental Biology at Berkeley in 1931. With Gladys Anderson Emerson, he reported the isolation of the pure Vitamin E from wheat germ in 1937. He also determined the formula CHO. Evans was also instrumental in developing reproductive systems research with Miriam Elizabeth Simpson and Choh Hao Li, by studying the oestrus cycle of rats. Evans is also credited with developing Evans blue, a method which determines blood volume in humans and animals.