The great epidemics that from time to time raged throughout Europe afford glimpses of the life and character of the people not readily obtained from other sources. Medical science recognizes to-day that the principal causes of such visitations are private uncleanness and the accumulation of filth in public places. During the Middle Ages, the regulations of sanitary police were wholly unknown. On every side heaps of garbage and putrefying offal met the eye and offended the nostrils. The necessity for the thorough ventilation and drainage of dwellings was unsuspected. The prejudice against bathing, which universally existed, was partly due to the example of the clergy, who were not supposed to have time to spare from their sacred duties to care for their persons, and partly due to contempt for the Mohammedans, whose lustrations were a peremptory religious duty. As Christianity spread, the practice of ablution gradually declined. The Roman thermæ, one of the wonders of the capital, were at first abandoned and afterwards utilized as quarries for the palace and the cathedral. A general idea prevailed that the ceremony of baptism removed all necessity for the subsequent application of water to the body. Filth became a test of devotion, and, following the example of their spiritual guides, the multitude came finally, by the natural law of association, to regard the unsavory manifestations of personal neglect as _prima-facie_ evidence of Christian orthodoxy. Thus, sanctioned by public opinion and confirmed by ecclesiastical authority, a stigma was placed upon cleanliness, and a premium offered for corporeal foulness and offensive surroundings. Those who violated the established custom were in danger of being denounced as heretics. It was one of the most serious accusations against the Emperor Frederick II. that he was addicted to the frequent use of the bath. Among the upper classes of society, the unpleasant consequences of untidy habits were in a measure neutralized by the excessive use of strong perfumes, such as musk, civet, and ambergris. Among the lower orders many of the physical conditions of life were indescribable. In the vicinity of towns, as well as of isolated habitations, equal negligence of the laws of health prevailed. From the moat, with its stagnant waters reeking with the refuse of the castle, to the vast marshes, with their exhalations poisoning the air around the hut of the shepherd, the atmosphere was charged with the miasma of death. When to the effects of such surroundings were added the depressing influences of contagion and terror, the results were appalling. The plague of the sixth century, whose course raged unchecked from the Bosphorus to the Atlantic, desolated entire countries; the Black Death of the fourteenth carried off seventy-five million persons, one-half the inhabitants of Christendom. So favorable to the spread of the pestilence were the climatic conditions of the