One of them is known as lutein and it has never been chemically isolated in its pure form.
"The Glands Regulating Personality"
Louis Berman, M.D.
The existence of lutein, like the existence of electricity, is an inference, something we are sure is there because of its effects.
"The Glands Regulating Personality"
Louis Berman, M.D.
But this leaves the question, what is lutein and why is it secreted?
"Hormones and Heredity"
J. T. Cunningham