HE fact that the air of sewers is freer from all forms of micro-organisms than is the outer air above them accounts for the immunity with which peo* ple may work in well ventilated sewers, and explains the reason why the great Paris sewers, for instance, are so safe, visited every year by thousands of travelers from all parts of the world, with no case on record of resulting disease. It has been related that the most remarkably located hotel in the world was built in these Paris sewers almost immediately beneath the Madeline church to accommodate the municipal scavengers. The interior was described as being singularly neat and clean, and as serving between sixty and seventy breakfasts and dinners to the workmen therein, and these sewer laborers are as healthy as are any other class of laborers in the city.

In view of all the facts, it becomes evident that the disconnecting trap and its vent are really worse than unnecessary. They are a positive injury as obstructing ventilation and waste discharge, as complicating the plumbing, as forcing odors generated in poorly ventilated sewers directly into the crowded streets, sometimes greatly to the annoyance of the people, and, above all, of depriving us of one of the most effective means now known of filtering the air of cities and towns of dust and disease germs. Their use should therefore be prohibited by law so that every soil pipe may serve as an effective means of ventilating the sewers and reducing the number of floating impurities in the outer air. This latter advantage .1 have not as yet seen advanced, though it is of the utmost importance, especially in times of epidemics.

The Disconnecting Trap And The Reasons Why Its Use 54

So important is this matter and yet so little is it understood by. the public that we ought to call a little further attention to some of the more recent investigations which have been made into the number and kind of bacteria found in the air of the streets and as to their fate when they find * access into the sewers through the ventilating inlets.

Analyses of the air in the Paris sewers have been regularly made at stated intervals and it is found that this air contains on the average more carbonic acid and ammoniacal nitrogen than the street air, but only half as many germs of any kind, while most of the investigators have failed to find any disease germs at all there. In these investigations it has been found also that the humidity in the sewers is great and practically constant.

In the air of the sewers of Berlin Petri found that there were only a very small number of micro-organisms as compared with that of the streets.

Similar results were obtained by other investigators in the sewers of London, Dundee, Westminster, Bristol and Sydney in Great Britain, where classifications of the various kinds of bacteria were made. In all these researches it was found that sewer air is, as far as germs are concerned, very much purer than outside air, and that these germs came not from the sewer but from the outer air; that a decrease in the number of germs in the outer air was followed by their decrease in the sewer air; that the kind of germs in the sewer air was the same as that in the outer air, but different from those contained in the sewage itself. Laws and Andrewes, who were commissioned by the county council to study the bacteria in the London sewers, state that the number of micro-organisms existing in sewer air appears to be entirely dependent upon the number existing in the outer air at the same time and in the same vicinity. They say that if the organisms existing in sewer air were derived from those existing in sewage, then the flora of sewer air should bear a very close resemblance to the flora of the sewage, but that they in reality bear no resemblance whatever to one another. They say, indeed, "we may go even further and state that, as far as we are aware, not a single colony of any of those species which we have found predominant in sewage has been isolated from sewer air. We consider, therefore, that the study of the sewage bacteria on which we have been engaged fully confirms the conclusions previously arrived at from the study of the microorganisms of sewer air, viz., that there is no relationship between the organisms of sewer air and sewage." * * * "In the conclusions to Part I of this report we endeavored to show that sewer air has no power of taking up bacteria from the sewage with which it is in contact . A strong argument in favor of this view is the fact that the very organisms which are most abundant in sewage are precisely those which are absent from sewer air. In the course of previous experiments on sewer air, the nature of the organisms in some 1,200 liters of sewer air was carefully determined. Not once was the bacillus coli communis or any of the predominant organisms of sewage found, though we have shown above that the former is present in sewage in numbers varying from 20,000 to 200,000 per cubic centimeter. If this be so, how infinitely improbable becomes the existence of the typhoid bacillus in the air of our sewers. That sewage* is a common medium for the dissemination

*This is before the disease germs are destroyed in the sewers by coming in contact with the other bacteria which find in sewage their natural element and which are non-pathogenic of typhoid is certain; that sewage-polluted soil may give up germs to subsoil air is possible; but that the air of sewers themselves should play any part in the conveyance of typhoid fever appears to us, as the results of our investigations, in the highest degree unlikely."

Now the house drains and soil pipes, being much smaller and longer in proportion to their sectional area, and being more uniformly moistened on their inner surfaces when in use, and having more bends and angles in proportion to their length than the public sewers, are correspondingly more effective in removing any bacteria which may enter them from the sewers. Hence the air of the house drains will, as is quite evident, and as I shall endeavor to make visible by experiments, be found to be still freer from germs than even that of the sewers themselves.