VENTILATION OF SEWERS is a thing which has given rise to much discussion. The simplest means are generally the best, and it is rarely the case in sewers that any improvement can be made over thoroughly good design and execution in the way of grade, alignment, and smooth inte riors. in some English cities ventilating shafts have been provided, but this has rarely if ever been done in America. Perforated manhole covers are about all the specific provision for ventilation made in the United States. The omission of traps at the foot of the house soil pipes will con tribute no small amount of ventilation, and is sometimes practiced. Objection to this plan is offered by some on the ground of danger to the inmates of houses if the soil pipes are converted into as many ventilating shafts, hut in properly designed and constructed sewers, having such ample ventilation as is thus afforded, there is a growing belief that no reason for apprehension will follow the practice. The 'sewer gas' of which so much was said some years ago does not exist—as a specific gas. Sewers, and particularly
those retaining deposits of organic matter for considerable periods, may yield various gases of decomposition, and under extreme conditions these gases may be positively and immediately dangerous. Numerous careful studies have shown that the bacterial contents of the air in sewers resemble those of the outer air above, rather than the baeteria in the sewage, and that they are comparatively few in numbers. In fact, the air in anything approaching a model sewer is better than that in overcrowded theatres and churches. The menace of sewerage systems is the pollution of public water supplies, not the air of either streets or buildings. Nevertheless, great care should be taken to prevent the ac cumulation of bad air in sewers and to reduce to a minimum the access of any sewer air to houses or other buildings.