But against the full significance of any epidemic, I am bound to tell you that these are but poor substitutes for protection. To render them effectual, even in their narrow sphere of operation, there must be great vigilance and great expenditure; a weary vigilance and a disproportionate expenditure, because chiefly given to defeat in detail what should have been prevented in principle. And be done what may, in this palliative spirit, the sources of the disease are substantially unstayed: for the faults, to which its metropolitan prevalence is due, consist not simply in a number of individual mismanagements, but include a common and radical mal-construction as their chief. No city, so far as Science may be trusted, can deserve immunity from epidemic disease, except by making absolute cleanliness the first law of its existence; such cleanliness, I mean, as consists in the perfect adaptation of drainage, water-supply, scavenage, and ventilation, to the purposes they should respectively fulfil; such cleanliness, as consists in carrying away by these means, inoffensively, all refuse materials of life--gaseous, solid, or fluid, from the person, the house, the factory, or the thoroughfare, so soon as possible after their formation, and with as near an approach, as their several natures allow, to one continuous current of removal. To realise for London this conception of how a city should cleanse itself may involve, no doubt, the perfection of numberless details. Yet, most of all, it would pre-suppose a comprehensive organisation of plan and method: not alone for that intramural unity of system which is needful for all the works, as most for those of drainage and water-supply; but, equally, to harmonise these works with other extramural arrangements for utilising to the country the boundless wealth of metropolitan refuse--for distributing to the uses of agriculture what is then rescued from the character of filth--for requiting to the fields in gifts for vegetation, what they have rendered to the town in food for man.