The Air of the City

WHEN, on that long-past burning August day, the wide-mouthed crater of Vesuvius poured down an overwhelming cloud on little Herculaneum and greater Pompeii, the daily life of rich and poor was choked out suddenly by that terrific burial in dust. As we pass from some fierce dust-storm in our cities, gasping and coughing with the load of dirt which has enveloped us, as we behold dark wreaths of heavy smoke pouring from soft-coal fires on every side, the thought must sometimes come that our communities to-day endure a peril far too much like that which in that distant time engulfed city and town about the Bay of Naples.

What does the air of the city hold ? How does it differ from pure mountain air? Wherein lie its dangers ? What can be found to remedy its perils ? All these are questions whose answers immediately concern every dweller in community centres. We know, chemically speaking, that air in its normal state is chiefly composed of oxygen and nitrogen, approximately one-fifth oxygen to four-fifths nitrogen. Besides these it contains some carbon dioxide, a little watery vapor, a few inert elementary gases, and small traces of compounds formed from nitrogen. How much do we know of the uses of those substances or of the wealth of life which the atmosphere holds? Day after day we go trudging to and fro along our various paths, at the bottom of a gaseous ocean which surrounds us, eating and sleeping, working with hand and brain, yet giving scarce a thought to the essential part which the air plays in our common life.

Of all the engines cunningly devised by man not one can equal that masterpiece of construction, the engine of the human frame. To run that engine, air is the first necessity. Construct it how you will, the greater part of the energy which feeds a power plant is lost before it reaches the applying machine. The body only has the power of using energy really economically and efficiently. Its food is its fuel. To be available, all the constituents of that food must be burned, producing heat and power. For that burning the oxygen of the air is essential. Equally true is it that nitrogen must be present to prevent the rapid combustion which would take place in oxygen alone. But whether the combustion be fast or slow, the action is the same. The body burns the carbon and hydrogen of its food and gives out the oxides of these substances, carbon dioxide (carbonic acid gas) and hydrogen oxide (water). The water that is formed within the body by the burning of hydrogen is of comparatively slight importance in a consideration of the vital questions of the effect of city air upon the individual, but the other factor, the carbon dioxide formed in the body, is of direct importance.

Farther and farther outward stretch the high city walls of brick and stone, — engulfing tree and shrub, — laying bare grassy knoll and living green. Higher and higher rise the chimneys, and with their rise increases daily the great outpouring of carbon dioxide and other gases, rushing into the air from the fuel burning in the fires below. Every type of fuel is carbon in its main essential, and every type chiefly produces carbon dioxide as the result of its combustion. Set a factory chimney in the midst of a grassy plain, or send forth huge volumes of hot gases from a steamer in mid-ocean, and the resulting carbon dioxide added to the air is of but little consequence. The wind scatters it to infinite dilution. The air of the city rising from hundreds of chimneys and confining walls has no such chance. The task is too heavy for even the sweeping winds to accomplish, robbed as they are of their chief helper in the disposition of carbonic acid gas, the living green of plant life.

Those city fathers who see nothing but æsthetic value in park or tree-lined boulevard, recognize not all the sanitary value of such breathing spots. Every leaf, every blade of grass, is a highly specialized factory for the care and disposal of carbon dioxide gas. Their growth, their very existence, depends upon the power possessed by their tiny cells to take that gas from the surrounding atmosphere and break it down into its component parts. That done, the carbon stays within the plant, forming its structure; the oxygen returns into the air, ready to unite once more wherever oxidizable materials are found. Every moment of every day the never-ceasing “ cycle of carbon ” continues on its round. The carbon of wood, coal, or plant, be it used for fuel or for food, is burned with evolution of the compound gas, carbon dioxide. That gas is seized by the plant, is separated, and once more assumes the simple form. The carbon which was the beginning is the end as well. The modern city, with its bricks and mortar, in most cases leaves but little room for these billions of plant factories. Its high walls bar the cleansing winds. Excess of carbon dioxide is but too likely to result.

In a most careful study of Air and its Relation to Vital Energy, Professor Woodbridge takes up this point in a light somewhat different from that in which it has been most commonly considered. Carbon dioxide gas exists in the air in far too small a quantity, even when materially in excess of the normal, to act in any way as a direct poison. It is in the effect of such excess upon the structure of the human frame that danger may lie.

The air of the lungs normally contains about a hundred times as much carbon dioxide as does the atmosphere around them. Our lung-bellows, by double action, produce the draft which keeps alive our body-fires and takes away the products of combustion, acting over the great surface of some four hundred square feet. Their boundary walls hold venous blood on one side air on the other. Through these walls the carbonic acid gas brought there by the blood passes into the air of the lungs, thence to issue with that air through nose and mouth. It is on the fact that the heavier carbon dioxide within the blood has a greater tension than the lighter air in the lungs, that the exchange depends. Lessen that tension, increase the heaviness of the air within the lungs by adding even a slight quantity of carbonic acid gas from the atmosphere, and the exchange may slacken. If the burned wastes of the body remain within the blood, they must clog the fires and produce disease. So finely are the body-fires adjusted that the least disturbance of normal conditions may tend toward injury. It cannot be denied that many scientists look upon the presence of carbon dioxide in excess in the air as of less importance than Professor Woodbridge imputes to it, yet in general the indication of the foulness of the air shown by carbon dioxide is considered of direct importance. In any case, where city walls, uncooled by oases of grass or trees, lie baking under our summer tropic sun, the gases from the city chimneys cannot but bear heavily on man and beast.

Device after device has been brought forward by inventors to secure a satisfactory regulation of temperature in houses and public buildings — cold-air regulators for furnaces, steam regulators for steam heaters, checks of various sorts. The principle of heat regulation in the body has been carried on for centuries effectively and well by three simple uniform methods. At high temperatures we perspire and evaporate the perspiration to cool the body. At medium temperatures we combine evaporation with variation of blood-flow, or change the condition of the vessels of the skin. At lower temperatures we must depend on increasing the body-fires to warm ourselves and burn our food more rapidly.

The variation of body temperature is affected by the outer cold or heat, by humidity or wind. Outside temperature, humidity, or wind, important as they are, can be but little controlled by city ordinances or private efforts. Wind is shut off by walls. Inside temperature errs, if anything, on the side of excess. Humidity is commonly overlooked altogether. The water vapor of the air conducts heat from the body more rapidly than dry air, and interferes with the evaporation of perspiration. Those two factors seriously disarrange the regulation of the body heat. The discomfort of the “ dog days,” as well as no small amount of the uneasiness of a crowded room, comes from the excess of water vapor in the air.

With the outpouring of the city’s chimneys has come another problem in these later days, a cloud which shadows all our cities, covering with its blackness wall and pavement, entering alike to house and factory, — the city’s smoke. Life in the soft-coal cities comes to be existence in a gray, blackened world. Whiteness of cloth, cleanliness of face or hands, becomes a shadowy hope, not a reality.

The reason for these conditions is by no means hard to find. Soft coal differs from hard coal most of all in this: when burned, its carbon, turning but in part to oxide, leaves a cloud of soft black soot, that carbon uncombined which soots the study lamp or rises from the snuffed-out candle. The coating which such soot casts on the lining of the lungs is one of the hardships of the city-dweller, despite the fact that our breathing organs possess a most extraordinary power of taking care of foreign bodies which invade their midst. Of all the particles that enter, no small portion returns, coughed back from the mouth or else ejected from the nose where tiny filters held them as they entered. Those which persist and lodge in windpipe or in bronchial tubes find there a horde of soldiers placed to drive the invader back, the cilia. These are cells shaped like tiny fingers, each finger fringed on its free end with a myriad of infinitesimal hairs which swing unceasingly through fife, and as they swing bear back and upwards towards the mouthinvading solids. Besides the cilia the phagocytes, those sanitary engineers of the blood, stand ready to seize, encompass, and destroy any harmful substances that may enter.

Yet through all these defenses solids can pass, and many do pass. Once in the lungs, they settle on the walls where passes out carbonic acid from the blood, where enters air carrying life-giving oxygen to the fires within. Where they fall, they clog the way. In city life, the fresh pink of a normal person’s lung is streaked and spotted with black lines which chart the blocked-up roads where breath of life once entered, where burned-out wastes once passed. In reason this may do no serious harm, because of the tremendous space through which the boundary walls extend. But as the coal-miner, from morning until night inspiring soft and clinging masses of black coal, dies long before his prime because his lungs, bounded by atrophied film, no longer serve their purpose, so the city-dweller, breathing day and night, year in and year out, an atmosphere charged with black smoke, shortens the course of life which should have been his own.

In smoky cities the proper ventilation of houses, one of the greatest essentials in stamping out tuberculosis, becomes more difficult. The doors and windows of the tenements are closed, and the stifled air within hastens disease and death. On humid days the smoke which fills the streets unites with the water vapor of the air to form the fogs which overhang the city. Fogs can exist only when the gaseous water of the air is liquified upon solid particles. The bits of carbon floating through the ways give such foundation, and the water condensing on them forms a mist. Probably without direct injurious effect, a fog depresses, renders resistance to disease more difficult, sets up a barrier to the cleansing, life-giving sun.

The pity of it is that all the evils which come from smoke are preventable. Smoke-consumers exist which have proved their worth. Due care in running fires will do much. No more fuel is required under careful management to produce combustion which shall be practically smokeless. These statements have been proved over and over again. It is a matter of community supervision, of laws rightly framed and fearlessly administered. Fortunately inspection is by no means a difficult matter. One city, for example, handles that problem by means of a chart holding six pictures of a chimney above a factory, the first of which shows the chimney with no smoke, the second with a light smoke issuing, the other four showing greater and blacker volumes. The first conditions are passable. The last are dangerous. The inspector takes a photograph of any questionable chimney and compares it with the standard pictures. The comparison tells the story. The factory is pronounced “passed,” or the owner is warned to conform immediately to the regulations, under penalty of the law.

The West as a whole is far beyond the East in its abatement of the smoke nuisance. In St. Paul some four years ago, the work was given over to the department of health, whose first act was to lay the following question before the local and national unions of steam engineers and firemen: “ Can the smoke nuisance as it exists to-day be reasonably prevented without injury to trade and manufacturing interests ? ” This question was unanimously answered in the affirmative by the members of both unions. Notice was taken of all dubious cases, and fines were imposed when necessary: a minimum fine of twenty-five dollars for the first offense, doubled for each succeeding one. The work has been most successful, and besides an abatement of smoke, a saving of fuel is reported.

In Milwaukee an ordinance which has gone through periods of relaxation and others of strict enforcement, has been successful when properly managed. About half the city at the time of a recent report used smoke-consuming devices; about one-fourth used hard coal or smokeless fuel. The general condition of the city was admirable. So admirable, indeed, that the title of the ordinance passed by the Common Council is worth quoting in full as an epitome of what such an ordinance should be.

An Ordinance declaring it to be a nuisance to cause or permit dense black smoke to be emitted from the chimneys or smoke-stacks of furnaces, boilers, heating, power or manufacturing plants, boats, vessels, tugs, dredges, stationary or locomotive engines, and creating the office of smoke-inspector, fixing his salary and prescribing his duties, and creating a board for the suppression of smoke.

Close as is the relation between the products of combustion and the public health, there is a yet closer one between the other burden which the atmosphere carries — dust — and disease. For many centuries the world believed that air was a vehicle of disease, and many a historian of pestilential years told of foul and heavy vapors which hung daily over doomed cities and seemed to carry death as they spread. From stage to stage passed the beliefs in the causation of epidemic disease, but with ever-recurring persistence they returned in one way or another to some belief in the transmission agency of the gases of the air. Only in that clarifying time when Schwann and Pasteur, Lister and Tyndall worked, was it made evident that the disease properties of the atmosphere came not from the air itself but from the burden of living organisms which it bore. From that great demonstration came the germ theory of disease.

In the rush of modern scientific research the work done a generation ago is likely to be lost to sight. It is well worth a moment’s pause, however, to recall the brilliant research by which John Tyndall, in 1868, proved the presence of organic matter in the air. Like many another experimenter, Tyndall found what he did not seek. He sought knowledge on the decomposition of vapors by light. He found the relation between dust and disease. The sunlight passing through a chink in the shutters reveals its path by the motes dancing in its ray. To obtain the results he wished, it was necessary for Tyndall to remove all floating matters from the air of his tubes. He attempted to do this in various ways, finally passing his air over the flame of a lamp. To his intense surprise the matter disappeared. It had been burned by the flame. His mind instantly leaped to the conclusion that it was organic matter, though practically every scientist had hitherto believed that the floating matter of the air was wholly inorganic and non-combustible. Tyndall created a living world at a bound, the world wherein moves the living matter of the air. He pushed his inquiry farther. He placed a lamp in a beam of light. Strange wreaths of blackness rose, blacker, as he says, “ than the blackest smoke ever seen issuing from the funnel of a steamer.” Carrying the inquiry on, he tried the same experiment with red hot iron, to preclude any possibility that the blackness might be smoke from a flame. “ The same whirling masses of darkness rose, — smoke was out of the question.” One conclusion remained. The darkness was that of stellar space, of the night which holds between the far-hung stars. The heat had burned the organic matter of the air, the inorganic had settled, no material substance remained to reflect light. Dust was in part organic. Nay, more. Dust was made up of two parts: the inorganic, matter like the rolling sands of the sea, the organic, germ masses of living organisms, infinitesimal, yet each complete in itself.

These micro-organisms of the air were soon proved capable of many things. Among other powers, they were proved to be carriers of disease. The surgeon’s scalpel laid on a dusty shelf had time after time introduced the germs of evil into the wound it was meant to cure. An operation was a dread event where death was almost as likely as recovery. Lister’s discovery of the possibilities of bacteriological cleanliness meant exclusion of germ-life from wound and instrument, from surgeon’s hand and winding bandage. It brought life to thousands. Swiftly the new theory made its way. Germ-life which could cause disease existed in the atmosphere. Methods arose to combat the various forms of ill which it brought. Knowledge grew as to the specific germs of evil and their brothers of good.

The marvelous life of the earth, the teeming billions of micro-organisms which inhabit the soil, have already been considered in “ City Water and City Waste.” ¹ It is sufficient to recall here that by far the greater part of the earth’s surface contains a vigorous microscopic life which serves many important purposes in the economy of nature. When earth is dried and driven by the wind about the streets, various types of microorganisms rise with the dust clinging to sand or splinter or floating by themselves. Of these forms, the bacteria interest us the most. The great service which they perform lies in the power which many of them possess of taking dangerous or exhausted organic material and turning it into harmless inorganic form. That service is turned to account in every modern sewage plant. The great injury which they may cause comes from a few forms in which lie the beginnings of disease. Growing with intense rapidity, these tiny plants, shaped like balls, rods, or spirals, spread wherever they may fall. Moist surfaces hold the germs, and besides the soil, they abound in manure and all decaying organic bodies, while those which find suitable homes in the human body multiply there with serious results. They appear in dust in billions piled on billions, when the dried earth, sweeping into the air with the varying impulse of the breeze, carries with it dried masses of bacteria.

The city street is a provider of bacterial hosts which has few equals. The concourse of the mart, the moving to and fro of many people, the constant throwing forth of human sputum, the dirt brought by the passing of many horses and domestic animals confined within a comparatively meagre space, all tend to furnish a constant supply of bacteria to the soil of the streets. When the soil has once been dried, the pounding of heavy wagons and the suction of the great wheels of motor cars form a fine pulverized surface powder on the road surface, ready to rise in clouds with every wandering breeze. The healthiest period which exists in city air is that during or just after a rain or snow. Moisture brings the germ content of the street most teeming with bacterial life to figures low in the extreme.

The germs which modern city air contains are chiefly of two classes. The first group affects the respiratory organs. Of these the tubercle bacillus, the bacterial form which underlies consumption, and the pneumococcus, the dreaded microorganism from which pneumonia comes, are chief. The second group embraces those diseases which are eruptive in their nature. Scarlet fever, measles, and the like send, with drying scales, their quota to the dust around.

To oppose the entry of these germs stands that same chain of defenses which the respiratory tract raises against invading coal-dust, and, as well, that continuity of armor which the body holds. Cased in the air-tight coverings of the skin without, lined with the barrier of the epithelia within, the human frame is well equipped by nature for the war against disease. Those coverings must be penetrated before disease can enter. A ragged sliver in the hand or foot often produces injuries far from proportional to its size. Why? Because the poisoned arrow of the Malay, though swifter, carries no more toxic poison than may come from a splinter of the streets. The danger of the dust lies, beyond all else, in the fact that every dust-storm, bearing thousands of small sharp grains of sand, tiny splinters of wood, and bits of stone, is a flight of poisoned arrows driven against the body covering of the passer-by. The poison which they bear may or may not come from the dried organic matter of the street. It may be lying at the point of entrance where the germs growing in the warm moisture of the respiratory tract lurk within the body like bandits beneath a fortress wall. In whatever way they come, it is most difficult for bacteria to pass through the body armor except when sharp particles such as those of dust make wounds or lesions in the inner walls. Once such openings are made, dangerous micro-organisms are but too ready to avail themselves of the opportunity. Once they are within, disease of major or minor type soon shows their presence.

Within the walls of dwelling, hall, or office-building, the direct dust-storm penetrates less easily, but only too often comes another danger from the difficulty of removing the fine cloud of dust which enters by every door and window from the streets, coating the furniture, hanging to curtain and rug and clinging there with a persistence which renders many a city home a veritable storehouse of ancient micro-organic life. Especially is this true where hangings of cloth, upholstered furniture, and heavy carpets furnish excellent abiding-places for the germs. Few sanitary reforms have meant more than modern hard-wood floors, light unupholstered furniture, and washable curtains.

One question must inevitably rise with any discussion of these points. “If such dangers exist about us in the city air which we all breathe, how can any escape ? ” It is easy to understand the freedom of individuals from specific contagion such as comes from impure water or impure milk. Disease from such causes can strike only in isolated spots or separate communities. It is far more difficult to understand the immunity which is afforded the Individual in the smokeand dust-laden air of thousands of American cities. Yet there is no question that great numbers show no signs of harm. Their vital resistance is so great as to make them triumphant over any form of disease. On the other hand, since there are thousands in any community who are susceptible to these attacks, it is the duty of the whole community to shield those thousands.

One germ found in dust needs especial mention. Tuberculosis, which may be classed among the dust diseases, ravages our country beyond all other plagues today. The consumptive sheds hundreds and thousands of living tubercle bacilli every time he sends forth sputum where it can mix with the dust of street or room. Once mixed with that dust, deposited on sand or other cutting particle, the poisoned weapon flies upward, ready to cut through and enter the body through the lesion formed in the lungs. In case after case we find in the lungs of perfectly healthy persons small tubercular lesions which have healed, showing that they were able to combat the poison when attacked. But how about the time of low resistance? How can the citizen tell when that time may come to him or to his family ? The magnificent crusade against tuberculosis is doing much to convince the individual of the necessity of care against scattering contagion. The municipality can do almost as much towards the stamping out of the plague by a steady constant struggle to achieve the cleanest possible street.

In the dirt of the assembly hall, of the theatre, of the hotel and the railway-car we find conditions in which the difficulties which exist in the private house are fourfold multiplied. For hours the crowds of people in such places sit breathing the accumulated dust brought from the streets, which, rising from the floor, floats in clouds into the air and settles heavily on the antiquated plush still in high favor for such places. It is but a year or two ago that the newspapers considered briefly the dangers of that bacterial paradise, the Pullman sleeping-car. A brief spasm of remonstrance passed over the country, and disappeared as suddenly as it came. The peril from such sources was, however, recognized two decades ago by more than one; and these words of Dr. Mitchell Prudden, concerning the presence of tuberculosis in such places, written almost as long ago, are no less true to-day: —

“ Sleeping-cars and the state-rooms of steamships and hotel bedrooms are almost always liable to contain infectious material, if they have been recently used by uncleanly consumptives or those ignorant of the danger of their expectoration. When the infectious nature of consumption becomes generally appreciated, hotels and transportation companies over long routes will be compelled to provide special accommodations for such persons as are known to be thus affected.”

Tuberculosis is but one of the contagious diseases which can be spread in this way. The outdoor treatment of tuberculosis is coming more and more to be recognized as consisting primarily of three things. First, — that the patient shall have an ample supply of good nourishing food. Second, — that the patient shall have an abundance of oxygen-laden air. Third, — that that air shall be as free as possible from bacterial forms. Climate and environment both seem to be secondary to these requirements, and the spread of outdoor treatment from its original field of tuberculosis to that of other respiratory diseases, such as grippe and pneumonia, is along the same line.

First of all steps to be taken in freeing the city from dust, is the laying of proper pavements. Most of our present pavements are little better than those of common country roads piled high in time of drought with shifting sands. So long as dry and unstable earth caps the broken stone of many a city street, so long the dust clouds will send many a patient to the doctors and the hospitals. The increasing use of the automobile will inevitably make proper street-cleansing easier. To-day the roads torn up by the suction of the huge machines show little promise of advance, but the future should tell a different tale. Continuous pavements like those of asphalt are ideal, because of their smoothness for motor carriage, and when the horse passes from the city, streets so paved will be wholly available. And the horse in time will have to go, as almost all the other wild and domestic beasts have disappeared from community centres. An anachronism in himself, the filth which follows him acts as a shelter for disease. With proper pavements, with the dirt of animals excluded, street-cleansing can be properly performed.

Within the house the vacuum-cleansing processes are sweeping out and completely removing from many a dwelling and public building the accumulated dust of years. In the vastly greater extension of such devices, in such increase of service as shall bring them within the constant use of every household, lies the great possibility here. City rooms will no longer be considered rightly ventilated by the dusty air of the sidewalk driven in by fans blowing through open windows. Satisfactory air-filters will take their place, filters not left to the intermittent, semi-annual care of a janitor. One watchword of the model city of the future will be “ Freedom from Dust.”

As the centres of population become more and more crowded, as the distance between the workrooms and the bedrooms of the city grows greater, more of our population burrow beneath the earth on their daily passing to and fro. The condition of the air in the subways of the cities has been a moot point since their first establishment. No subway has undergone more criticism in this respect than has the long winding tunnel which lies beneath New York. The trouble began with the first opening of the subway, while its stifling heat during the terrific summer of 1905 is a matter of painful memory to thousands. That heat was made yet more intolerable by the peculiar “ subway smell.” From those causes grave questions inevitably arose as to the healthfulness of the air within the subway. Those queries have now been answered in large part by an investigation made by Dr. George Soper, which considered temperature, humidity, odor, bacteria, and dust. The first two of these divisions, important as they are, have comparatively little relation to our theme, but the last three are pertinent.

The belief in the injurious effects of the odor of the subway was a relic from the period when certain forms of illness were supposed to be directly connected with evil smells. With the exception of the ill effects which certain gaseous compounds of sulphur and carbon produce, there seems to be scarcely any ground for relating disease and evil odor. Constant exposure to any smell, be it bad or good, is likely to produce nervous irritation and exhaustion. On the great rose-farms of southern France for example, the stranger wandering among the fragrant fields soon feels the same heavy headache which a persistently objectionable odor like that of a soap factory is likely to produce. A lowering of energy from any type of odor may put the individual into a condition to invite disease, but is little likely to be the direct cause of contagion. In the case of the subway, the odor came chiefly from the smell of the trap-rock employed in the stone ballast of the road-bed, mingled with lubricating oil and gear grease, and combined with occasional slight infusions of human odor. Disagreeable as it might be when long inhaled, there was no reason to believe it dangerous.

The dust of the subway was quite another matter. It was very distinct from the dust of the streets, blacker, more clinging. As a horseshoe magnet was brought near a heap of dust the powdery mass sprang into magnetic curves. Following this line, two magnets of similar size were hung, one in the subway and one in an iron foundry; and the first showed clusters of black magnetic stuff far heavier than the second. Analysis after analysis showed almost half as much dust again by weight in the subway as was found outside. Over sixty per cent of that dust was iron. A passenger traveling for half an hour inhaled on an average some .42 of a milligram of the dust, a very appreciable amount, and received into his lungs a goodly number of iron missiles. Add to them the tuberculosis germs forever floating in the cars, and you have a very dangerous combination. The iron came from the wearing down of the brake-shoes on the wheels, and it is computed that the huge figure of twenty-five tons of iron and steel is ground into powder in the New York Subway in the course of a mouth. Here is a type of dust almost wholly disregarded up to the present time, which may mean much in the tuberculosis campaigns of the future.

The bacteria found in the subway were commonly less in number than those found outside, but amounted to the fairly high figure of some five hundred thousand per gram of dust, sometimes running as high as two million. The passenger waiting for the train, however, was engaged in no more harmful occupation so far as danger was concerned than he would have been if waiting for a car on the street outside.

In summing up the situation, the engineer in charge states: “ My own conclusion was that the general air (of the subway) although disagreeable was not actually harmful, except, possibly, for the presence of iron dust.” An investigation of that exception is now going on, and it is the opinion of no small number of engineers that the word “ possibly ” in the quotation just made is likely to be stricken out.

One other point concerning subway air should be mentioned. The constant renewing of the atmosphere by the motion of the trains keeps the carbon dioxide in the tunnel so little more than that on the surface that, on that account, no more injury should be charged against the subway than against the streets.

Of all the odors and gases which were considered perilous by sanitarians of an older day, sewer gas stands preeminent. The average citizen looks upon sewer air, or leaky joints in his plumbing, with more fear than he would upon a perfect bath of tubercle bacilli or a glass of water filled with typhoid germs. To a research recently completed at the Massachusetts Institute of Technology we owe much of our latest knowledge of the subject. During a period of over three months a current of air was passed through sewage under varying conditions, and the flight upward of the bacteria was noted. That was done in order to answer the following question: “ What is the bacterial condition of the atmosphere where sewer air is present ? ”

Without considering the ingenious and effective way in which the experiments were carried on,we may pass immediately to the results; in brief they follow. With a very strong current of air it is possible to drag a few dangerous bacteria from sewage lying in a trap, and take them fifteen feet or more up through a drain. Even under the most favorable conditions, however, the number of germs so pulled upward is very small. Ordinary sewage contains something like three-quarters of a billion per litre of the organisms studied. In the maximum case, not forty of this vast number were found to have risen through the drain. The result of this research must lead us to believe that carriage of disease germs from a housedrainage system is extremely improbable.

There is, however, one record of an even more recent investigation which stands in opposition to these conclusions. Major Horrocks of England has recently concluded a study of a similar type in which striking results were obtained. Certain specific classes of bacteria not found in the atmosphere about the place in which the experiments were carried on, were drawn upward by currents of air through traps in drain-pipes. Remarkable results were obtained. The tiny organisms were found in large numbers, spread from one end of the building in the military hospital to the other. Results so unusual as these, and so contrary to most modern conclusions, should be noted.

But no single experiment to-day can be taken as absolutely conclusive, either for or against. Especially is precaution wise, since there remains one further possibility. Can sewer gas so debilitate the human system as to prepare it for the inroads of disease? That remains a subject for further investigation, and, until that is settled by longer arid more rigorous experimentation, it is wiser to be on the safe side and keep to thoroughly conservative plumbing regulations.

The whole problem of the air of a city tends to fall under certain definite headings : excess of carbonic acid, the smoke nuisance, the dust evil, the problem of sewer gas. For each, the city can provide a remedy. Limiting the height of buildings, widening the narrow streets, providing parks and squares with green trees, grass, and shrubs will do much toward diluting, scattering, and removing excess of carbon dioxide. Laws passed, and enforced, requiring smokeconsumers and proper firing will absolutely do away with the smoke nuisance. Proper pavements, with good streetcleaning, will diminish germ-laden dust to a minimum. Proper plumbing regulations will guard us from any possible danger from sewage in our houses.

It is all in the city’s hands. Community life is apparently the inevitable sequence of our modern age. The fortunate who can, the intelligent who know, will turn more and more for their hours of recreation and of sleep to wide stretches of heath and hill, or to the comparative cleanliness of the suburbs. But for the thousands of the narrow streets the cleansing of the city air is a necessity. To every pallid weary worker should come the rushing breath of purifying winds, the free and open air of heaven.