By thus keeping the streets clean, it will also be practicable to sprinkle them through the day, during the dusty season, and thereby to moisten the heated air to its normal condition, and refresh the exhausted bodies of the inhabitants. Every city should inaugurate such a system of sprinkling the streets.

The fire departments of every city, having a plentiful supply of water, can very easily extend their functions so as to effect this cleaning and sprinkling of streets. All the cities along rivers, for instance, can without much cost have their streets every day regularly washed from the water-plugs arranged for the fire-engines. As matters stand at present, people wait for a heavy rain to accomplish this. But heavy rains do not come at our bidding, and light ones only make the condition of our streets worse. It behooves man to help himself, and not wait upon the irrational forces of nature, that may send down a heavy rain when it is a positive injury, and withhold the moisture when all the earth cries for it. We must learn to control this, and provide by art against the irregularity of the action of natural forces.

The soil being, next to the air, the most active agent in spreading disease and epidemic matter, it is evident that the soil-water of cities and villages, their springs and wells, must be generally of an unhealthy character, and unfit to be used for drinking purposes. Hence public water-works are very essential for the preservation of health, and their construction and use should be insisted on wherever this is at all practicable. But, besides their great sanitary value as furnishing the best drinking water, they are indispensable for the purposes of drainage, for watering the streets and parks, and all the vegetation of a city, and for the establishment of public baths.

Gas-works, with their constant efflux of sulphureted hydrogen, should never be tolerated within the city limits; and in the laying of gas-pipes it should be seen to, that they are put at as great a depth as practicable under the ground, and made tight and secure against the escape of gas. Indeed, all factories that emit foul odors, and poison the air, should be removed far from the city and disinfected daily.

Nor should slaughter-houses be tolerated within the city, and the strictest control should be exercised over them to secure the removal of all noxious matter and the disinfection of their offal. The public health of every city demands that a rational system of abattoirs should supersede the present miserably unsystematic arrangement of

slaughter-houses, with their inevitably accompanying nuisances of soap, fat, etc.; establishments concerning which the New York Board of Health says: It is positively asserted that more noxious gases escape into the air from this source than would result from the decomposition of human bodies if the whole island were a grave-yard.” It makes one blush to reflect that these life-destroying establishments are still tolerated in the midst of large cities, when so far back as the reign of Henry VII. a petition was addressed to the king, from several parishes of the city of London, affirming that the said "parishes were greatly annoyed and distempered by corrupt air engendered in the said parishes by reason of the slaughter of beasts had and done in the butchery of St. Nicholas;" which petition called forth an enactment that "no butcher or his servant is to slay any beast within the walls of London, or any walled town in England, under a penalty."

CHAPTER V.

CONSTRUCTION OF BUILDINGS WITHIN THE CITIES.

Apart from what is above required for the city at large, a general building-law should be passed for the erection of all new buildings in the city; and another law requiring that all buildings already erected should be made conformable to the laws of sanitary science, so far as practicable.

For executing such a building-law, two classes of commissioners should be joined in a board to be appointed,-architects and sanitary officers. The architectural commissioners will have to see that the necessary architectural requirements for buildings are complied with, as to thickness of walls, strength of foundations, fire-escapes, fireproof externally, etc.; the sanitary commissioner, in conjunction with the architect, should supervise the sanitary requirements, such as the height of the building itself, of its several stories, of its windows, and their position in regard to light and fresh air; the water-closets, and their proper connection with the general sewer; the construction of the kitchen, with reference to cleanliness, absorption or removal of all fumes, stenches, etc., and immediate removal of all offal and dirt;

the proper supply of bath-rooms; and such a system of ventilation and disinfection as the exigencies of the building may require, and as I have already pointed out to some extent in the chapter on Pure Air.

To cut off as much as possible communication between the house and the soil, the floors and walls of every cellar and basement should be made as air-tight as possible, and the habitation of cellars and basements should be absolutely forbidden.

This fact of sanitary science, namely, that the soil under the house is as capable of conducting impure air, pregnant with disease, into the house, as the air outside of the house, is also one of those circumstances that are very little known and still less heeded, even by experienced architects. Dr. Pettenkoffer remarks in relation thereto : "Remarkable testimony as to the permeability of the ground, and of the foundations of our houses, has been given by gas emanations into houses which had no gas laid on. I know cases where persons were poisoned and killed by gas which had to travel for twenty feet under the street, and then through the foundations, cellar-vaults, and flooring of the ground-floor rooms. As these kinds of accidents happened only in winter, they have been brought forward as a proof that the frozen soil did not allow the gas to escape straight upwards, but drove it into the house. I have told you already why I take the frozen soil to be not more air-tight than when not frozen. In such cases the penetration of gas into the houses is facilitated by the current in the ground-air caused by the house. The house, being warmer inside than the external air, acts like a heated chimney on its surroundings, and chiefly on the ground upon which it stands, and the air therein, which we will call the ground-air. The warm air in the chimney is pressed into and up the chimney by the cold air surrounding the same. The chimney cannot act without heat, and the heat is only the means of disturbing the equilibrium of the columns of air inside and outside the chimney. The warm air inside is lighter than the cold air outside, and this being so, the former must float upward through the chimney, just like oil in water. It continues to do so as long as fresh cold air comes into its neighborhood from outside. As soon as we interrupt this arrival, the draught into the chimney is at an end. Any other way of looking at the action of chimneys leads to erroneous views, which have many times stopped the progress of the art of heating and ventilating.

If

"Thus our heated houses ventilate themselves, not only through the walls, but also through the ground on which the house stands. there is any gas or other smelling substance in the surrounding ground-air, they will enter the current of this ventilation.

"The movement of gas through the ground into the house may give us warning that the ground-air is in continual intercourse with our houses, and may become the introducer of many kinds of lodgers. These lodgers may either be found out, or cause injury at once, like gas; or they may, without betraying their presence in any way, become enemies, or associate themselves with other injurious elements, and increase their activity. The evil resulting therefrom continues till the store of these creatures of the ground-air are consumed. Our senses may remain unaware of noxious things which we take in, in one shape or another, through, air, water, or food.

"We took rather a short-sighted view all the while, when we believed that the nuisances of our neighbors could only poison the water in our pumps; they can also poison the ground-air for us, and I see more danger in this, as air is more universally present and more movable than water. I should feel quite satisfied if, by my lectures, you were convinced of this important fact, if of none other.

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Hereby the question about the origin of the gas is certainly not yet answered, and would have been left equally unsettled if we had to ask: Whence comes all the carbonic acid which is found in the ground-water? All this water is precipitated from the atmosphere, from rain or snow. In entering the soil as meteoric water, its amount of carbonic acid is exceedingly small. By help of Bunsen's analytical tables it is easy to calculate, from the quantity of carbonic acid in the atmosphere and the absorbing power of water for this gas, that one pint of rain-water at the average temperature and barometrical pressure can contain only a very small fraction of a grain of carbonic acid; and this has been proved further by analytical experiments. But this analysis of the pump-water in Munich, which was poorest in carbonic acid, showed that it contained on an average 11 to 1.9 grains of free gas. The ground-water at the places of examination stands about sixteen feet from the surface. It is therefore evident, that the meteoric water, which is the sole source of the ground-water, must more than centuple its original amount of carbonic acid before it reaches the wells. This much is certain: that the source of the carbonic acid must be sought for in the soil, and

for this reason the more natural supposition is, that the soil yields the gas and gives it to the water and to the air simultaneously, but naturally with greater facility and in greater quantity to the air than to the water. The sources of the carbonic acid in the soil have now to undergo a stricter investigation; the probability is, they owe their origin to organic processes in the soil."

But, furthermore, the habitation of any new dwelling within three months after its erection, though it be purified by fire in each room and in the cellar, should be forbidden, as the enormous quantity of moisture which new walls, etc., contain cannot evaporate before that time, and during its presence renders such dwellings dangerously unhealthy.

It having been clearly demonstrated, that the natural ventilation of buildings by windows, chimneys, and other vents is altogether insufficient to meet the requirements of the human body, an artificial system must be prescribed, whereby the necessary quantity of pure air can be brought into every room of each house and the impure air constantly expelled. The revolving hot and cold air furnace accomplishes this object, and ought, therefore, to be required for all large cities by the general building-law.

All buildings should be inspected semi-annually by the official architectural and sanitary commissioners, both in regard to their safety and their healthfulness, and the result published and reported; the report to specify all particulars, and to state the number of inmates, so that the overcrowding of houses and rooms, which makes proper ventilation impossible, and spreads diseases and crimes in so many portions of our large cities, may be effectively prevented.

It

In the erection of high buildings in cities, with many large windows of plate and other glass, external shades above the windowtops should be provided, to prevent as far as practicable the radiation and reflection of the solar rays, and avoid the increase of heat that will add several degrees to the natural warmth of summer. has been conjectured, though perhaps without sufficient grounds, that an extensive refraction of the solar rays from plate-glass in midsummer might affect the regularity of the ebb and flow of the electromagnetic tides, and increase the formation of carbonic acid gas in the air of a badly ventilated city; but whether these injurious effects arise from this cause or not, the fact that it increases the natural