The Sanitary Problems of New York City.—Professor W. P. Trowbridge, discussing "The Sanitary Problems of New York City," in the "School of Mines Quarterly," considers chiefly the ventilation of houses and the condition of the streets. The topography of the city, presenting long rows of closely built blocks of dwellings and stores, and of the narrow streets that separate them, is a very obvious sign of the close crowding of a large population into a small space which actually exists. This crowding is of itself a great sanitary evil. If, says Professor Trowbridge, we may take a lesson from nature in the distribution of other classes of the animal kingdom, we find that the herding together in confined places of any one class of animals is detrimental to the health and well-being of the individuals. Diseases peculiar to the class of animals are apt to arise, and a general physical deterioration takes place. "As an animal, man is not exempt from this law of nature, unless, through his own superior intelligence, he secures to himself immunity from the evils which over-crowding entails." A momentous question in our city life is whether, in the construction of our houses, and stores, and hotels, and public halls, the quantity of air which each person requires for his health is provided for by processes or appliances of ventilation. The quantity of air required for a healthy life is generally estimated by the number of cubic feet needed for respiration alone. This is a mistake. Each person needs vastly more—enough to secure a thorough aëration of his clothing and to destroy by oxidation all the hurtful emanations of the body. In houses, moreover, the needs of large quantities of pure air for the aeration of clothing, basements, kitchens, closets, and the closets in which clothing is kept, are probably as great as for respiration. Yet, "how few of the houses in the long blocks which constitute the city of New York have been constructed with the slightest reference to the constant introduction and removal of air!" All of our houses are provided with four or five chimney-flues which might be made available for ventilation to a certain extent, but in the use of which it is so little thought of that the rooms, that might be connected with them, are hermetically sealed from them. The kitchen or basement, where there is necessarily an accumulation of deleterious gases, or impoverished air, is perhaps the worst ventilated room in the house. The people still need to be convinced that ventilation is necessary, and that force must be used to move the air. The object can be secured by means of vertical ventilating flues of sufficient suction, but the application of heat either by a gas-jet or other artificial means is requisite to keep them in operation. The matter of the dirt in the streets has an important sanitary aspect. From this point of view, Professor Trowbridge thinks it is worthy of consideration whether an entirely new treatment is not advisable. Heretofore, attention has been confined to the removal of the dirt as it accumulated; Professor Trowbridge would have means adopted to prevent its accumulating. "The dirt that covers the streets as they are now paved does not come entirely from above or from any external source, but is forced upward from beneath the pavements by the impact of the trucks, carts, carriages, and horses' hoofs, in the ordinary traffic of the city. It is doubtful whether it is possible to keep the streets reasonably clean, even with an expenditure of double the present outlay for that purpose. The soil on which the pavements are laid is not a soil which effects its own drainage, and each successive shower or storm saturates the surface beneath the paving, the water carrying down the leachings of the streets; and this soil, permeated with decomposing substances and saturated with polluted water, is forced to the surface. No better medium for retaining and giving off malarial gases could probably be manufactured. When dried, this expelled mud becomes dust, and is carried about by the winds into every household. The real cure of this great evil appears to me to be an impervious pavement—an asphaltic pavement." No dirt could rise through this, and, if every street in the city were paved with it, what dirt falling upon it was not carried off naturally by showers into the sewers could be thoroughly removed by mechanical sweepers without dust or noise.