One turns with quite a degree of relief to the momentous work of Birnbaum[13] on the Psychoses of Degeneracy. As far as can be ascertained the author does not endeavor to subdivide his degenerative states into so many types and forms. According to him, the essential characteristics of the degenerative psychoses--namely, the extraordinary determinability and influence which outside impressions have upon the disorder, the mode of genesis and the psychological evolution of the delusions, etc.,--may be attributed to the essential ear-marks of the degenerative character; that is, to the exaggerated auto-suggestibility, the great instability of the existing conditions and mental pictures, the disharmony between the perceptive and imaginative capacities and the preponderance of a lively fantastic coloring to the dry thinking of these individuals. They do not form disease processes of a definite characteristic form, but episodic psychotic manifestations on a degenerative soil, and the manifold phases of the collective forms are to be considered as repeated fluctuations about the psychic equilibrium of these individuals. He further noted that the symptomatology of these disorders remained limited to a relatively well systematized delusional fabric, which, however, in contradistinction to paranoia, does not persist for any length of time, but disappears for certain definite reasons. They do not form any typical symptom-complex. The delusional ideas may take on any character; hallucinations may occur in all fields of the sensorium; consciousness may or may not be clouded, but is usually so in the beginning of the disorder. Recoveries are as a rule gradual, but may set in quite suddenly. Insight may or may not be present. The course of the disorder, like its symptomatology, offers nothing of a definite, characteristic nature.
Thus we see that the distinguishing feature of Birnbaum's degenerative psychoses does not lie in their mode of appearance, in their symptomatology, but in the mechanism of their evolution, and, above all, in their total dependence upon extraneous influences. They are typical psychogenetic disorders, the psychic etiology of which is potent not only in the incitation of the processes, but in the modeling and fashioning of them. Although Birnbaum notices the close relation that exists between these psychoses and the hysterical psychotic manifestations, he would separate them distinctly from hysteria.