This deviation, even if, at the outset, it was ever so slight, contained transmissible elements of such a nature that anyone bearing in him the germs becomes more and more incapable of fulfilling his functions in the world; and mental progress, already checked in his own person, finds itself menaced also in his descendants.’[4].

He sees in the fashionable society of Paris and London that "[e]very single figure strives visibly by some singularity in outline, set, cut or colour, to startle attention violently, and imperiously to detain it.

Nordau establishes the cultural phenomenon of fin de siècle in the opening pages, but he quickly moves to the viewpoint of a physician and identifies what he sees as an illness[undue weight?

The Philistine, however, regards them as a passing fashion and nothing more; for him the current terms, caprice, eccentricity, affectation of novelty, imitation, instinct, afford a sufficient explanation.

The purely literary mind, whose merely æsthetic culture does not enable him to understand the connections of things, and to seize their real meaning, deceives himself and others as to his ignorance by means of sounding phrases, and loftily talks of a ‘restless quest of a new ideal by the modern spirit,’ ‘the richer vibrations of the refined nervous system of the present day,’ ‘the unknown sensations of an elect mind.’ But the physician, especially if he have devoted himself to the special study of nervous and mental maladies, recognises at a glance, in the fin-de-siècle disposition, in the tendencies of contemporary art and poetry, in the life and conduct of men who write mystic, symbolic and 'decadent' works and the attitude taken by their admirers in the tastes and aesthetic instincts of fashionable society, the confluence of two well-defined conditions of disease, with which he [the physician] is quite familiar, viz.

[11] This phrase would find itself incorporated into psycho-physiognomy, a pseudoscientific belief that an individual's mental and "moral" health were determined by the shape or dimensions of their face; this would play a crucial role in developing concepts of scientific racism and eugenics.

Notable critics would include Sigmund Freud, who remarked in his 1905 work Three Essays on the Theory of Sexuality that "It may well be asked whether an attribution of 'degeneracy' is of any value or adds anything to our knowledge."