With all the advance in preventive medicine we can not hope to avoid disease entirely.  We are discovering that the sources of disease are on all sides of us, and so omnipresent that to avoid them completely is impossible.  If we were to apply to our lives all the safeguards which bacteriology has taught us should be applied in order to avoid the different diseases, we would surround ourselves with conditions which would make life intolerable.  It would be oppressive enough for us to eat no food except when it is hot, to drink no water except when boiled, and to drink no milk except after sterilization; but these would not satisfy the necessary conditions for avoiding disease.  To meet all dangers, we should handle nothing which has not been sterilized, or should follow the handling by immediately sterilizing the hands; we should wear only disinfected clothes, we should never put our fingers in our mouths or touch our food with them; we should cease to ride in public conveyances, and, indeed, should cease to breathe common air.  Absolute prevention of the chance of infection is impossible.  The most that preventive medicine can hope for is to point out the most common and prolific sources of infection, and thus enable civilized man to avoid some of his most common troubles.  It becomes a question, therefore, where we will best draw the line in the employment of safeguards.  Shall we drink none except sterilized milk, and no water unless boiled? or shall we put these occasional sources of danger in the same category with bicycle and railroad accidents, dangers which can be avoided by not using the bicycle or riding on the rail, but in regard to which the remedy is too oppressive for application?

Indeed, when viewed in a broad philosophical light it may not be the best course for mankind to shun all dangers.  Strength in the organism comes from the use rather than the disuse of our powers.  It is certain that the general health and vigour of mankind is to be developed by meeting rather than by shunning dangers.  Resistance to disease means bodily vigour, and this is to be developed in mankind by the application of the principle of natural selection.  In accordance with this principle, disease will gradually remove the individuals of weak resisting powers, leaving those of greater vigour.  Parasitic bacteria are thus a means of preventing the continued life of the weaker members of the community, and so tend to strengthen mankind.  By preventive medicine many a weak individual who would otherwise succumb earlier in the struggle is enabled to live a few years longer.  Whatever be our humanitarian feeling for the individual, we can not fail to admit that this survival of the weak is of no benefit to the race so far as the development of physical nature is concerned.  Indeed, if we were to take into consideration simply the physical nature of man we should be obliged to recommend a system such as the ancient Spartans developed, of exposing