If once it be accepted that health, capacity, endurance, and energy are more powerful weapons for a progressive people than are sword or gun, obedience to these commands will be general and their results enduring. The pages of history teach us that each nation in turn has exhibited these qualities at its zenith of success, whether it were the relatively highly civilised inhabitants of Greece and Rome, or the barbarian hordes under Attila. They characterise equally each group of successful pioneers, whether they be the Pilgrim Fathers of the sixteenth, the Huguenots of the seventeenth, or the successful colonist of the nineteenth century. When however their cultivation is neglected the force of the life current of a people or community is lost; the mighty river of a nation's prosperity dwindles to an insignificant streamlet of mere existence, soon to be lost to view in the morass of oblivion. To what general causes may such deterioration be attributed? Among the more prominent must be mentioned ignorance of man's physical nature and of the nurture essential to his welfare; subtle forms of self-indulgence; lowered standards of morality; enervating luxury, or, in some cases, so severe a struggle for existence among the salt of the population (the upper, middle, and professional classes, superior mechanics and artisans), that even patriotism does not justify a quiverful of children. But the persistence of these causes is a national calamity. It is the science and art of hygiene which is emphasising their disastrous consequences. No longer in its infancy, no longer a mere collection of fads, questionable statistics, and empirical doctrines, hygiene is prepared to inform us how to promote human efficiency in every relation of life--domestic, occupational, social, and imperial. Its tenets are firmly based upon a goodly group of sciences, and their utilisation call into play a whole range of arts. Its theories find confirmation in the social problems of the day, and the experience gained from their tentative and partial application affords sound evidence of their worth to the world. The "expectation" of life, for instance, has been extended ten years in half a century; in twenty years the death-rate has decreased thirty per cent. Disease has been found in most instances to be controllable, and has been controlled; unhealthy occupations have had their dangers curbed if not entirely banished, and the lot of many has been immeasurably brightened. _Yet_ the weak joints in the nation's harness are gaping, and the vigour and virility of the masses appear to be diminishing. Again we ask, Why? III. STAGES IN THE GROWTH OF SANITARY SCIENCE