{123} Insanity may, both in its acute and chronic form, be the result or symptom of simple anomalous excitation or nutrition of the brain or of inhibition of some of its portions, without any change in its gross appearance which can be detected by our present methods of research. In the majority of cases there are found diseased conditions which become more manifest the longer the duration of the disease, appearing for the most part in the blood-vessels, pia mater, and cortex of the brain, but also in the medullary portion, many of which are recognized only in their late stages. In the functional mental diseases there is no characteristic lesion of the brain as yet recognizable, even in the latest stages, more than is to be found in the brains of persons dying from other causes. When apparently local injuries or diseases cause insanity, they probably do so through a general disturbance of the brain or through diffuse disease resulting therefrom and for the most part affecting both hemispheres. The molecular, chemical, anatomical, physiological, pathological, or physical changes in the brain which give rise to insanity, and their relation to the grosser pathological conditions of the brain, are still not clearly made out. In terminal dementia, especially in the last stage of paralytic dementia, nearly every tissue and organ of the body may be found to have undergone pathological changes, of which by far the greater portion is secondary to disease of the brain; and it is impossible to say how much of the brain lesions in these and other conditions of mental unsoundness is secondary to the disease or an accidental complication. DIAGNOSIS.—In the diagnosis of insanity the physician assumes a responsibility for which he is liable under the common law. It is important, therefore, to avoid mistakes as far as possible. In the majority of cases the patient's unsoundness of mind is evident before he is brought to the doctor, but in not a few the symptoms are obscure, and they are often rendered more difficult of correct understanding and appreciation by the deception or reticence of the patient and by the prejudices of his friends.