Mankind has always been equally fascinated and horrified by the specter of mental illness, which explains in part the phenomenal successes of the pop oversimplifications. But, as always, there's a dearth of solid and accessible works like this one. Dr. Snyder, who is Professor of Psychiatry and Pharmacology at Johns Hopkins, strikes a fine balance between sophistication and generalization in this overview of what researchers and clinicians now know about the prevalence, varieties, specific symptoms, biological and sociological causes, and chances for recovery from that still mysterious cluster of maladies we call mental disease. His book is extremely well-organized within the three basic if sometimes overlapping categories of neurosis, depression and schizophrenia, and includes a digest of the variety of therapies available. He devotes a chapter to the understanding of suicide, the unthinkable ""final solution,"" which Snyder contends ranks with heart disease and cancer as a leading cause of death--though often it is accomplished in disguised form. His particular emphasis is on Freud and his disciples, but the book also discusses controversial theorists like Janov (whose ""Primal Scream"" he considers a high risk) and Laing (given to ""hyperbole"") as well as the merits and drawbacks of group. Basic, authoritative and sympathetic.