gard to the passage of disease-germs through traps, and concludes as follows:

"The liquids in all these tubes and flasks, though kept from two to five months at cultivation temperature, have remained perfectly clear, and even when examined with a lens multiplying nine hundred diameters, exhibited no trace of life. The conditions of these experiments seem to me crucial, and to warrant the conclusion that germs do not pass through a sound water-trap. If no germs pass through, then it is certain that no particles pass through, because the particles in a soil-pipe are putrid, and because the passage of organic particles through water necessarily Fig. 3—A Pot-Trap, showing how Water escapes by Siphonage. impregnates them with germs. Clearly, therefore, such particles as epithelium from the bowels in typhoid fever, containing the typhoid contagia, are cut off and effectually excluded from the house by a sound water-trap. Water-traps are, therefore, for the purpose for which they are employed—that is, for the exclusion from houses of injurious substances contained in the soil-pipe—perfectly trustworthy. They exclude the soil-pipe atmosphere to such an extent that what escapes through the water is so little in amount and so purified by filtration as to be perfectly harmless; and they exclude entirely all germs and particles, including, without doubt, the specific germs or contagia of disease."

The testimony of these distinguished scientists must be regarded as conclusive in the absence of contradictory evidence. Is there such evidence on record? Let us examine the authorities. It is claimed that different results have been obtained in a few instances by other investigators. Some years ago, Prof. Doremus showed that gases would pass through water from one test-tube to another. But it must be remembered that the gases used in these experiments were in a highly concentrated form. Such conditions as were then imposed are absolutely impossible outside of the chemical laboratory. The atmosphere of sewers, drains, and soil-pipes is in reality ordinary air containing less than one per cent of the gases and particles given off by decomposing sewage. The results of over sixty analyses made by such men as Dr. Letheby, Dr. Miller, of London, and the late Prof. Nichols, of Boston, show an average of only four tenths of one per cent of carbonic acid with mere traces of sulphureted hydrogen, marsh-gas, and ammonia. The putrid organic vapors, and the putrefactive