result, for example, of a rapid flow along the drain into which the waste-pipes discharge, and, under these circumstances, sewer-air and its organic ingredients pass unhindered into our houses. So, also, traps are liable to be forced by the pressure of the sewer-air upon them. Having regard to some of Dr. Carmichael's experiments, it might at first sight be supposed that organic particles contained in bubbles of air would be detained in their passage through a water-trap. This, however, is by no means the case. In certain experiments carried out at the Royal Institution by Professor Tyndall, F. R. S., it was found that air, passing through an experimental tube, carried with it "a considerable amount of mechanically suspended matter." Dr. Carmichael freely admits the inadequacy of water-traps as they exist, and points out many dangers attendant upon them. He enforces the caution he gives by a case related in a report of Dr. J. B. Russell, Medical Officer of Health for Glasgow. In certain tenements of one apartment, having no connection with the sewer, there had been a death-rate from diphtheria of 12, and from enteric fever of 24·9, per hundred thousand inhabitants. The introduction of a sink increased the diphtheria death-rate to 25·3—i. e., 110 per cent—and from enteric fever to 67·7—i. e., 171 per cent—the rate of mortality from certain allied diseases also undergoing a corresponding increase. Not knowing whether there were other circumstances that favored this special incidence of disease upon these tenements, I should find some difficulty in asserting that the drain-connection was the cause of the whole of the increase in the diseases specified; nevertheless, Dr. Russel's opinion that it was, carries great weight.
One striking instance, which further illustrates this point, came under my own cognizance. Some years ago I received instructions to inquire into the cause of an outbreak of enteric fever in a small township in Yorkshire. The main incidence of the disease was upon a group of houses, which formed an irregular square, containing twenty-three cottages, occupied by eighty-eight persons. Up to the first week in June the inhabitants of this locality had been free from fever, but at that date a series of attacks of well-marked enteric fever occurred almost simultaneously in a number of houses, fresh attacks taking place day by day until, in the space of a few weeks, one or more inmates in fifteen out of the twenty-three cottages had been attacked, the number of patients amounting to thirty-five. Now, when the contagium of enteric fever is conveyed by water, the persons attacked are generally attacked almost simultaneously. There is, however, in the case of enteric fever, a definite interval, generally of some ten to fourteen days, between the reception of the poison into the system and the occurrence of symptoms of the disease. The water-supply which these families generally used in common was a well in the neighboring field; but this had been disused for a period which more than covered the "period of incubation" above referred to.
