The most significant contribution to the study of isolation from the sociological standpoint has undoubtedly been made by Fishberg in a work entitled _The Jews, a Study of Race and Environment_. The author points out that the isolation of the Jew has been the result of neither physical environment nor of race, but of social barriers. "Judaism has been preserved throughout the long years of Israel's dispersion by two factors: its separative ritualism, which prevented close and intimate contact with non-Jews, and the iron laws of the Christian theocracies of Europe which encouraged and enforced 'isolation.'"[116] 3. Isolation and Personality Philosophers, mystics, and religious enthusiasts have invariably stressed privacy for meditation, retirement for ecstatic communion with God, and withdrawal from the contamination of the world. In 1784-86 Zimmermann wrote an elaborate essay in which he dilates upon "the question whether it is easier to live virtuously in society or in solitude," considering in Part I "the influence of occasional retirement upon the mind and the heart" and in Part II "the pernicious influence of a total exclusion from society upon the mind and the heart." Actual research upon the effect of isolation upon personal development has more of future promise than of present accomplishment. The literature upon cases of feral men is practically all of the anecdotal type with observations by persons untrained in the modern scientific method. One case, however, "the savage of Aveyron" was studied intensively by Itard, the French philosopher and otologist who cherished high hopes of his mental and social development. After five years spent in a patient and varied but futile attempt at education, he confessed his bitter disappointment. "Since my pains are lost and efforts fruitless, take yourself back to your forest and primitive tastes; or if your new wants make you dependent on society, suffer the penalty of being useless, and go to Bicêtre, there to die in wretchedness." Only second in importance to the cases of feral men are the investigations which have been made of the results of solitary confinement. Morselli, in his well-known work on _Suicide_, presented statistics showing that self-destruction was many times as frequent among convicts under the system of absolute isolation as compared with that of association during imprisonment. Studies of Auburn prison in New York, of Mountjoy in England, and penal institutions on the continent show the effects of solitary incarceration in the increase of cases of suicides, insanity, invalidism, and death.