“Mens conscia recti in corpore sano,” is Horace’s well-known description of the happy man. Lucretius appears to have formed a correct estimate of the most important bodily and mental conditions on which our happiness depends:— “O wretched mortals! race perverse and blind! Through what dread, dark, what perilous pursuits Pass ye this round of being! Know ye not, Of all ye toil for, Nature nothing asks, But for the _body_ freedom from disease, And sweet unanxious quiet for the mind?” Like human beings, the sciences are closely connected with, and are mutually dependent upon, one another. The link in the chain may not be apparent, but it has a real and palpable existence. Medical and moral science are more nearly allied than we should, _à priori_, conclude. We speak of the science of medicine, not the practice of it; for, like judgment and wit, or, as the author of the School for Scandal ironically observes, like _man and wife_, how seldom are they seen in happy union. Garth feelingly alludes to this unnatural divorce:— “The healing art now, sick’ning, hangs its head, And, once a _science_, has become a _trade_.” Psychological medicine has been sadly neglected. We recoil from the study of mental philosophy as if we were encroaching on holy ground. So great is the prejudice against this branch of science, that it has been observed, that to recommend a man to study metaphysics was a delicate mode of suggesting the propriety of confining him in a lunatic asylum! In order to become a useful physician, it is necessary to become a good metaphysician; so says a competent authority. It was not, however, Dr. Cullen’s intention to recommend that species of philosophy which confounds the mind without enlightening it, and which, like an _ignis fatuus_, dazzles only to lead us from the truth. To the medical man we can conceive no preliminary study more productive of advantage than that which tends to call into exercise the latent principle of thought, and to accustom the mind to close, rigid, and accurate observation. The science of mind, when properly investigated, teaches us the laws of our mental frame, and shews us the origin of our various modes and habits of thought and feeling—how they operate upon one another, and how they are cultivated and repressed; it disciplines us in the art of induction, and guards us against the many sources of fallacy in the practice of making inferences; it gives precision and accuracy to our investigations, by instructing us in the nicer discriminations of truth and falsehood.