Some account of the structure and functions of the human frame, of the action of physical agents on this wonderful machinery, and of the principles which relate to Individual, as well as to Public Health, ought to form a part of elemental education. There is a growing conviction that the necessity for such knowledge is not restricted to the physician; that it is essential also to the educator, the mother, the nurse, and indeed to every one who would enjoy, together with the due development of his physical, intellectual, and moral nature, the full term of the boon of life. The main causes which shorten and embitter human life, as far as that unhappy result depends on the disturbance of health, are within our own control. There is the closest connection between the knowledge we have acquired of the physical conditions on which the life and health of individuals and communities depend, and on our command over those conditions. Every fact we have learnt respecting the great laws of nature, on our conformity to which our very existence depends, has taught us that the circumstances which produce excessive sickness and early death are preventible. The character of Pestilence which gave it its great power and terror—that it walketh in darkness,—is its character no longer. Its veil has fallen, and with it its strength. A clear and steady light now marks its course from its commencement to its end; and that light places in equally broad and strong relief its antagonist and conqueror—CLEANLINESS. * * * * * The term Epidemic has become a popular one. It is derived from two Greek words, which signify “upon the people—prevalent among the people”—diseases which, at one and the same time, prevail extensively among large masses of the people. Recently these diseases have received another name, which is also becoming familiar—“Zymotic,” from a Greek word, which signifies to “ferment,” as if the efficient cause of these diseases, whatever it may be, acts in the manner of a ferment. Epidemic diseases, though called by a common name, present great differences in their external characters. Plague, Yellow Fever, Cholera, Small-Pox, Typhus, Scarlet Fever, Influenza, present characters so definite and special, that they have been naturally regarded as distinct diseases, and they really are so different as to render it desirable, for many reasons, that each should be discriminated and denoted by its proper name. Amidst this great diversity in form, however, they present very striking resemblances, of which the following are generally recognized:— 1. Epidemics resemble each other in being all fevers. They all exhibit that particular assemblage of symptoms which from time immemorial it has been agreed to denote by the term Fever. This is as true of the great Epidemics of former times as of those which prevail in our own.