_Remarks_: The badly-tainted patient is originally psycho-sexually abnormal, in that, in character and in the sexual act, he feels as a female. This abnormal feeling remained purely a psychical anomaly until three years ago, when, owing to severe neurasthenia, it received overmastering support in imperative bodily sensations of a _transmutatio sexus_, which now dominate consciousness. Then, to the patient’s horror, he felt bodily like a woman; and, under the impulse of his imperative feminine sensations, he experienced a complete transformation of his former masculine feeling, thought, and will; in fact, of his whole vita sexualis, in the sense of eviration. At the same time, his ego is able to control these abnormal psycho-physical manifestations, and prevent descent to paranoia,—a remarkable example of imperative feelings and ideas on the basis of neurotic taint, which is of great value for a comprehension of the way in which the psycho-sexual transformation may be accomplished. _IV. Degree: Metamorphosis Sexualis Paranoica._—A final possible stage in this disease-process is the delusion of a transformation of sex. It arises on the basis of sexual neurasthenia that has developed into neurasthenia universalis, resulting in a mental disease,—paranoia. The following cases show the development of the interesting neuro-psychological process to its height:— Case 100. K., aged 36, single, servant, received at the clinic on February 26, 1889, is a typical case of paranoia persecutoria, resulting from neurasthenia sexualis, with olfactory hallucinations, sensations, etc. He comes of a predisposed family. Several brothers and sisters were psychopathic. Patient has an hydrocephalic skull, depressed in the region of the right fontanelle; eyes neuropathic. He has always been very sensual; began to masturbate at nineteen; had coitus at twenty-three; begat three illegitimate children. He gave up further sexual intercourse, on account of fear of begetting more children, and of being unable to provide for them. Abstinence proved very painful to him. He also gave up masturbation, and was then troubled with pollutions. A year and a half ago he became sexually neurasthenic, had diurnal pollutions, became thereafter ill and miserable, and, after a time, generally neurasthenic, finally developing paranoia. A year ago he began to have paræsthetic sensations,—as if there were a great coil in the place of his genitals; and then he felt that his scrotum and penis were gone, and that his genitals were changed into those of a female. He felt the growth of his breasts; that his hair was that of a woman; and that feminine garments were on his body. He thought himself a woman. The people in the street gave utterance to corresponding remarks: “Look at the woman! The old blowhard!” In a half dreamy state, he had the feeling as if he played the part of a woman in coitus with a man.