"To communities as well as to individuals there is nothing so expensive, so fatal to prosperity, as sickness. To a productive and labouring community, health is the chief estate.... A community is but a system of individuals--if one portion of that system be disabled by sickness, every other portion will feel the blow; the whole community will be taxed to support that part which is rendered incapable of supporting itself. It is then a plain matter of self-interest, as well as of solemn obligation, to exercise the most vigilant care in preserving to the poor their only worldly possession, their health and capacity for self-support." Nor did the danger to the great community of London, from the prevalence of sickness in any particular district, appear to have received the faintest recognition. And yet, in the matter of health, and protection from infection, all classes from the highest to the lowest had equal interest; for disease commencing or raging in one district is not long in spreading to other districts. The Medical Officer of Health for Chelsea (1857-8) wrote:-- "It cannot need any argument to prove that diseases of an epidemic or infectious nature cannot be arrested in their progress by the imaginary line drawn around the boundaries of the parish--that the smoke from the furnaces in Lambeth and Vauxhall must be wafted across the Thames and influence the health of the inhabitants of Chelsea, if not kept in check, and that evils of minor importance in Pimlico, on one side, and Kensington on the other, may be quite as prejudicial to the health of the neighbours residing on this side of the boundary as to those among whom they are generated." That any one locality had a duty to its neighbours, still less to London as a whole, as well as to the people of its own area, was beyond the range of the ideas of the vestries and district boards. Indeed, if their sense of duty did not induce them to look after and safeguard the people for whose sanitary condition they were immediately responsible, how could it be expected of them to be influenced by considerations as to those residing outside their area, and residing many miles away. And yet, by the very condition of things, this greater responsibility did exist. But the great fact that in the vital matter of the public health London was one great community, the various parts thereof being indissolubly welded together into one great whole, had not as yet apparently dawned upon the minds of the newly-created local authorities; nor, indeed, had Parliament even realised it, for it had left the forty and more of those authorities full freedom to scatter disease of the deadliest type from one end of London to the other, and to imperil the lives of London's inhabitants.