IN RECENT years a great deal of work has been done on the psychologic aspects of mental disorder. The literature which has accumulated is enormous. Many writers have ignored the obvious fact that etiology is a complex question, that causes are multiple, and have said loosely that mental illness is psychologic or emotional in origin. A smaller, but persistent voice has also been raised, saying that much could be learned through biologic chemistry. Not much has been done about it but gradually good work in this field is accumulating. Folch 1 read a paper at the opening of a new research laboratory at the McLean Hospital in May 1946. He reviewed the contributions chemistry had made to psychiatry and outlined plans for the future. He explained that the brain has certain unique features: (1) lack of a lymphathic system, (2) abundant blood supply, with poor vasomotor control, (3) high consumption