THE Annual Report, 1935–36, of the Joint Board of Research for Mental Disease of the City and University of Birmingham contains an account of much painstaking and laborious work (Birmingham: The University, 1936). The occurrence and distribution of 80 named varieties of micro-organisms are tabulated; 6,565 specimens were examined. Somewhat optimistically the report claims to have solved the problem of the cause of mental disease, since “it appears that mental disorder cannot be classed as an infectious disease, nor as a metabolic disorder, but that it is a clinical resultant of infectious and metabolic disorders acting during any period of the ante- and post-natal life of the individual, thus determining the character and onset of the mental symptoms”. Also, “The functional disturbances of the central nervous system responsible for the symptoms of mental disorder, can be clinically and pathologically associated with local disturbances of the vascular supply to certain vital centres of the brain”. It is true that the pathology of some brain diseases that cause mental disorder is well established,. for example, encephalitis, syphilis, tumours; but there still remains a host of disorders, ranging through hysteria and the anxiety and obsessional states to schizophrenic personalities, and cyclothymia or manic-depressive conditions and paranoia, that have so far defied the laboratory expert.