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only interest, but must engage the loyal support of every good American. Yet the name itself means the same to no two people, and there exists an equally diverse opinion respecting the relative importance of the component elements of the public health, and the causal influences controlling it. However, it is unnecessary to bring up disputed points and impractical discussions when there are issues of the most vital concern involved in this question.

The public health, or the health of people en masse, in groups or communities, is more than an adding together of the conditions of health in which each person in the group finds himself. Just as the mob-sense, the group consciousness, or the dominant spirit of the mass, as one chooses to call it, differs from the individual personalities which compose it, so the public health differs from the individual health of each single person. The public health is intangible, though none the less real. It is not a static condition, which can be moved and delimited from without, but it is full of dynamic potentialities, and pregnant with unforeseen complications and denouements. The study of it leads into a bewildering array of intimately related subjects which at first glance seem to bear but a meager relation to it. A survey of its field must begin with an understanding of what is included in the term public health itself.

Public health may be considered to present itself in three phases, as physical, mental and social health. Each is influenced by many factors.