having made a series of careful experiments, assisted by B. W. Thomas, President of the State Microscopical Society, and in the presence of O. C. De Wolf, M. D., Commissioner of Health for that city, they have given it as their concurrent opinion that, as at present constructed, water-traps do not prevent the passage of "disease-germs" into our houses. Dr. De Wolf takes pains to especially emphasize the fact of "the readiness with which organic germs pass through the water of a sewer-trap and are thrown off from the free surface into the atmosphere of a room." (See "Report of the Health Department, City of Chicago, April 15, 1881.")
But, although I can not speak as an expert in this matter, it will be permitted me to say that there seems no reason, even if other and conflicting experiments had not been made, why the experiments of Carmichael should be regarded as conclusive. That unwholesome gases did not pass through well-sealed and ventilated traps, at a certain time and under certain circumstances, in sufficient quantity to imperil life, and that organic germs were excluded wholly, furnishes no conclusive evidence that they might not pass through at another time and under other circumstances. The amount of vapor, ah', and gas contained in the sewers is greater at one time than at another. Their elasticity and tendency to escape are varied according to the nature and amount of the gases generated; according to the temperature, which is changed continually where pipes are in use by the alternate flow of hot and cold water; and according as the gases are moved upward with more or less force by the direction and strength of the aerial currents through the drains. In our own city, and in other maritime cities, and upon the sea-coast generally, the action of the tides in obstructing the outflow, and thus driving the contents of the sewers back toward the houses where the pipes terminate, is often enormous, and such as, by the most ample provision for escape through ventilators, can not always prevent a sudden pressure upon the water-traps sufficient to displace their contents, or to force the gas through the water in the form of bubbles, or, finally, to increase the capacity of the water to receive the sewer-gas by absorption.
Muhlenberg says, "The bacillus typhi has been found in drinking water"; and Dr. Janeway, addressing the Academy, said: