As has already been pointed out, the danger from the inspiration of sewer air is generally believed to lie in predisposing the system to harm from disease germs coming from other sources. This predisposition is probably due to the gases given out by putrid fermentation, such as carbonic acid, ammonia, sulphurated hydrogen, hydro carbons and volatile fatty acids, and the danger is in proportion to the concentration of these poisonous matters. This danger may be reduced to a minimum or altogether removed by thorough ventilation. In order to provide a simple ocular demonstration of the manner in which sewage and the moist surfaces of sewers arrest these fine particles when they are brought in contact with them, gradually clearing the air of them entirely, I constructed several experimental drain pipes of metal and glass tubing and of different lengths, varying from ten to twenty-five feet, some being straight and others bent.

These pipes were thoroughly moistened on the inside with water, and a specified quantity of dry fine dust was placed at one end of each, and the attempt was made to blow the dust through the pipes from end to end by means of bellows. Before describing our experiments it is important to point out the relation which dust bears to disease and how it serves to disseminate bacteria through the air. Mrs. Frankland* says in her most valuable work, entitled "Bacteria in Daily Life," published in 1903: "That it is no exaggeration to describe streets from the bacterial point of view as slums is to be gathered from the fact that much less than a thimbleful of that dust which is associated with the blustering days of March and the scorching pavements of summer may contain from nine hundred to one hundred and sixty millions of bacteria. But investigators have not been content to merely quantitatively examine street dust; in addition to estimating the numerical strength of these dust battalions, the individual characteristics of their units have been exhaustively studied, and the capacity for work, beneficent or otherwise, possessed by them has been carefully recorded. The qualitative discrimination of the bacteria present in dust has resulted in the discovery of, among other disease germs, the consumption bacillus, the lockjaw or tetanus bacilli, bacteria associated with diphtheria, typhoid fever, pulmonary affections and various septic process. Such is the appetizing menu which dust furnishes for our delectation. There can be no doubt, therefore, that dust forms a very important distributing agent for microorganisms, dust particles, aided by the wind, being to bacteria what the modern motor-car, with its benzine or electric current, is to the ambitious itinerant of the present day. Attached to dust, bacteria get transmitted with the greatest facility from place to place, and hence the significance of their presence in dust."

*Mrs. Percy Frankland, Fellow of the Royal Microscopical Society, Honorary Member of Bedford College, University of London, and joint author with Professor Frankland of "Micro-Organisms in Water," "The Life of Pasteur," etc.

It is also now believed that typhoid fever may be spread by dust, the germs having been discovered in it. A typhoid fever epidemic at Athens a few years ago was believed on good evidence to have been spread by the wind on typhoid dust particles, and epidemics of typhoid in other places have recently been traced to the same cause, the dejecta of sufferers from the disease having been thrown in places where it became dried and afterward distributed by the wind.

"That the bacillus of consumption," says Frankland, "should have been very frequently found in dust by different investigators is hardly surprising when it is realized that the sputum of phthisical persons may contain the tubercle germ in large numbers, and that until recently no efforts have been made in this country to suppress that highly objectionable and most reprehensible practice of indiscriminate expectoration. Considering that the certified deaths from phthisis in 1901 in England and Wales only reached the enormous total of 42,408, and bearing in mind the hardy character of the bacillus tuberculosis when present in sputum, it having been found alive in the latter even when kept in a dry condition after ten months, it is not too much to demand that vigorous measures should be taken by the legislature to cope with what is now regarded as one of the most fruitful means of spreading consumption."

Boards of health and high authorities both here and abroad have stated that tuberculous sputum is the main agent for the conveyance of the virus of tuberculosis in the air from man to man, and that indiscriminate expectoration should therefore be suppressed.

Dr. E. Concornotti has recently made a very elaborate study of the distribution of disease germs in air, with the result that out of forty-six experiments in which the chacter of the bacteria found was tested by inoculation into animals, thirty-two yielded organisms which were pathogenic.

Messrs. Valenti and Terrari-Lelli found similar results in their systematic study of the bacterial contents of the air in the city of Modena. In their report they state that the narrower and more crowded the streets the greater was the number of bacteria present in the air, and the more frequently did they meet with varieties associated with septic disease.

Schaffer has shown that leprosy bacilli may be disseminated in immense numbers by the coughing of leprosy patients, while it has been estimated that a tuberculous invalid may discharge a billion tubercle bacilli in the space of twenty-four hours, and the dried sputum of consumptive persons has actually engendered tuberculous symptoms in the lungs of animals which were made to inhale it. In as many as 71 per cent of bovine tuberculosis cases the respiratory organs were the seat of the disease. A case is mentioned by the well known veterinary authority, M. Nocard, of a whole stall of animals becoming infected through the workman attending them being consumptive. He slept in a loft over the cows, and his tuberculous sputum in the form of dust was conveyed to the stalls beneath and so spread the infection. The disease is known to have been spread, on the other hand, from animals to men in the same way.*