and employed in these places, in the filthy occupation of glue and music-string making, &c., enjoy an immunity from disease that is truly astonishing, while their exemption from illness during the destructive prevalence of cholera in Paris was equally remarkable. The existence of such disgusting nuisances, as represented by Duchatelet, can by no means be approved of; but reference to them is made here to show, by well-ascertained facts, that the remedying of the effluvia arising from imperfect drainage, cesspools, _et hoc genus omne_, is not of such VITAL importance as the free admission of the atmosphere; for we have seen that stagnant air is caused by the want of a free current, and that it is rendered more humid than usual by the non-admission of light (which is heat), and further that that humidity increases the activity of noxious gases, so that where ventilation is defective, there will always be an accumulation, and consequently a concentration, of the gases from cesspools, exhalations from the body by expiration, and from the skin; all these facts, physiologically considered, will show the vast importance of the access of light and of pure air, on which all sanitary measures, to be effective, must be based. Ventilation, by striking at the root of the mischief, will remedy all its evil consequences. Again, it must be recollected that the object of ventilation is not solely to dissipate and get rid of odours offensive to the olfactories, but also to supply the system with a vital stimulus--the very _pabulum vitæ_--the oxygen necessary for the proper performance of the functions of the different organs, which cannot be obtained in due proportion from stagnant air--the supply in such an atmosphere from defective circulation being inadequate to the demand or consumption. When an animal is inclosed in a limited quantity of atmospheric air, it dies as soon as the oxygen has been consumed; and no other air will maintain animal life but oxygen, or a mixture which contains it in a certain proportion. Further, ventilation, by supplying the vital stimulus, and inducing a normal condition, also fortifies the system against atmospheric vicissitudes--the grand excitant of disease. Opening up and enlarging drains, or establishing them where none had previously existed, while the localities are allowed to remain in a crowded state, will, while such operations are being carried on, multiply the evil. A commencement must be made by rasing to the ground the dens of physical and moral iniquity which have been so disgracefully permitted to exist in the occupancy of those unfortunates who have it not in their power to remedy the miseries to which it never was the intention of Creative Wisdom that the meanest reptile should be subjected, much less Man, once the image of his Creator,--His noblest work! The subjects of Light and Air having been disposed of, we will next discuss the properties of Water: