But, in order to understand how this prolific cause of evil acts on the human race, it is necessary not only to look to the draining, sweeping, and cleaning of streets, courts, and closes, but to enter the houses, and attend to the "conditions of existence" of their inmates, in the lowest and most unhealthy portions of all our great towns. When we do this, we find that, in all those houses which are the chief seats of epidemic disease, there are congregated together in small and dirty rooms such masses of destitute human beings, usually ill-clothed and inadequately protected from cold, that it is mere mockery to speak of improving the atmosphere of their rooms, especially during the night, by any appliances to the streets or courts from which they are entered, or even by any means of ventilation to which, at least in cold weather, the inmates will submit. It is even in vain that we issue directions for the cleansing of the rooms, or regulations, in the case of lodging-houses, for limiting the number of persons to be taken into them, or that we form model lodging-houses, in which a certain number of persons may be decently accommodated. All such measures have a good effect on a certain number of the people; but those among whom the epidemic diseases are always found making most progress have no means of availing themselves of these advantages: they can no more pay for clean or well-aired rooms than they could pay for any of the luxuries of civilised life. "Their state of destitution binds them firmly to one description of locality," and forces them to congregate together in masses, necessarily implying such a contamination of the atmosphere in which they live, as no such measures can counteract for six hours.