When a state or municipality has so far advanced in civilization as to consider it desirable to take measures to protect the public health by preventing individuals from polluting the air or water liable to be used by {208} their neighbors, etc., the services of the medical profession are always called upon. The foundation of public hygiene is information as to the occurrence of certain forms of disease, the cause of which can be referred with more or less precision to a certain limited locality. This information may be very imperfect, consisting of little more than rumor and opinions as to the existence of an undue amount of sickness or mortality in a certain place, or it may consist of precise reports setting forth the number of deaths from each cause, the proportion of each of these to the population by age, sex, occupation, etc., and of the whole to births--constituting what is commonly called the "vital statistics of a place"--and also of reports of the occurrence of certain preventable diseases; and between these two the information may be of various degrees of completeness, but, whatever there be, it is for the most part obtained either directly or indirectly from medical men. The reliability and completeness of the information thus obtained by the state determines to a great extent the direction and character of the work done in destroying or preventing the causes of disease, and it is also an important means of increasing our knowledge with regard to the nature of these causes. The character of this information depends largely upon the character of the physicians who furnish it. In a large part of the country medicine is legally in the position of any common occupation; that is, the term "physician" is defined as applied to "any one who publicly announces himself to be a practitioner of this art, and undertakes to treat the sick either for or without reward." Under such circumstances there can be no guarantee that all who call themselves physicians are properly qualified or competent to furnish reliable information for registration purposes, and, as a matter of fact, a large number are not so qualified. It is for this reason that there is such a close connection between public health authorities, registration of vital statistics, and the registration of those physicians whose certificates as to causes of deaths, etc. will be accepted by the state; and hence the nature of the public health organization of a state and the personnel of its officials are matters of great importance to physicians. On the other hand, the efficiency of a public health service depends very largely upon the relations which it holds with, and the light in which it is regarded by, the medical profession. A health officer who is distrusted and disliked by the physicians of his district cannot effect much unless he can overcome this feeling, and his tenure of office must always be very insecure.