learned so much, but for equal surprise that so many persons appear to think it a complete and full-grown science, and that it is entitled to speak with confidence on all the great mysteries of the earth that have been hidden from the generations before us. Such being the newness of man and of his science of the earth, it is not too much to say that humility, hard work in collecting facts, and abstinence from hasty generalization, should characterize geologists, at least for a few generations to come.

In conclusion, science is light, and light is good; but it must be carried high, else it will fail to enlighten the world. Let us strive to raise it high enough to shine over every obstruction which casts any shadow on the true interests of humanity. Above all, let us hold up the light, and not stand in it ourselves.

INLETS FOR INFECTION.*

By R. THORNE THORNE, F. R. C. P.

IN selecting a subject to bring before you, I felt that I should not be trespassing beyond the lines indicated by the committee who have organized this series of lectures if I addressed my remarks to some points connected with those specific fevers the prevention of which must be regarded as coming within the scope of sanitary administration. I may, perhaps, indicate the importance of such a subject by quoting a few figures from the reports of the Registrar-General of England. Limiting myself to those diseases the spread of which is admittedly to be controlled by the adoption either of efficient sanitary works, or of such sanitary measures as isolation and disinfection, I find that during 1871-'80 the following deaths were registered in England and Wales: From typhus fever, 13,975; from enteric or typhoid fever, 78,421; from simple continued fever, which when fatal is probably nothing less than an ill-defined form of enteric fever, 25,643; from diphtheria, 29,425; and from scarlet fever, otherwise called scarlatina, 174,232. These deaths are essentially due to diseases which may be called preventable, and they amount in all to 321,696 in the ten years. But the influence of these diseases upon the population can not be judged of by the death-roll alone. For every fatal case there have probably occurred at least ten non-fatal attacks, and thus we come to be confronted with a total of 3,538,656 attacks from the preventable specific fevers. Mr. Simon, C. B., F. R. S., in dealing with such death returns, has said: "Of the incalculable amount of physical suffering and disablement which they occasion, and of the sorrows and * Abridged from a leature delivered at Cheltenham, March 15, 1883, and published in "The Practitioner."

anxieties, the often permanent darkening of life, the straitened means of subsistence, the very frequent destitution and pauperism, which attend or follow such suffering, death statistics, to which alone I can refer, testify only in sample or by suggestion."

The means by which infection is likely to be conveyed to households are far too numerous to be dealt with in a single lecture, and I have thought it best to select for consideration three or four of what I feel to be among the more important, and to deal with these in detail.

In a report on an epidemic of enteric fever at Croydon, in 1875, Dr. Buchanan, F. R. S., makes use of the following words: "The air of the sewers is, as it were, 'laid on' to houses." That significant expression "laid on " comes in aptly, as giving prominence to the special features of one of the channels for conveying infection to households, to which I propose drawing your attention. From the inside of every ordinary dwelling-house there pass certain waste-pipes intended to convey liquid refuse, first to the house-drains without, and thence to the public sewers. It is the custom to regard these conduits as passing from house to sewer, but this evening I would ask you to compare them with the pipes for the supply of coal-gas, and to view them rather as passing from the sewer as a center to the periphery within our dwelling-houses. In our comparison the public sewer may be regarded as corresponding with the gasometer; the house-drain and the waste-pipes as representing the service-pipes for gas; and the so-called "trap" indoors as taking the place of the metal tap found in connection with each gas-bracket. Sewer-air, even in its normal state, is a grave source of danger to health; but when the sewers receive in their course along the streets the infectious refuse discharged from houses where specific disease prevails, then the sewer-air-harmful hitherto is changed into an intense poison.

How is it usually sought to debar this poisonous agent from dwellings? The sole means adopted, in nine cases out of ten, consists in placing at some point of the pipe which connects the interior of the house with the interior of the sewer a small body of water which is known as a trap," and which is designed to act as a barrier to the passage of all sewer-air. The contrivance most commonly resorted to is the so-called bell-trap, an apparatus in which the rim of a bellshaped cup is suspended in a small body of water contained within a circular depression. This form of trap is of all the least efficient; it is not only one in which the water-lock constituting the trapping may at any moment be entirely removed at the will of the individual, but at its best it provides between the house and the sewer a layer of water only about one half or three quarters of an inch in depth. Even the most efficient of all traps, the so-called "siphon-bend," is not much better. Dr. Andrew Fergus maintains that trapping has but little effect in keeping sewer-air out of houses, as the entrance of the con

taminating air is not so much due to occasional and temporary failure in the efficacy of the trap as to an almost constant absorption of sewerair by the water on the sewer-side of the trap, and its subsequent discharge from the house-side. Dr. Fergus has made a series of experiments in a glass tube so bent as to resemble the ordinary "siphon" trap, and charged with water. Certain gases were evolved on what we may call the sewer-side of the trap (b), and tests were applied to ascertain whether the gases succeeded in passing through the water. The results as tabulated by Dr. Fergus are as follows:

It was, however, urged that the results would probably be different if the trap were ventilated. A ventilating-shaft (c) was, therefore, inserted in the upper part of the bend on the sewer-side, and the experiments were repeated. "The results," says Dr. Fergus, "were much the same, except that the reaction was a little longer in showing itself."

Ordinary sewer-air may be taken to contain in every hundred parts about seventy-nine parts of nitrogen, nearly twenty of oxygen, not quite half a part of carbonic acid, and traces of sulphuretted hydrogen, marsh-gas, and ammonia. These gases, however, when inhaled in the proportions indicated, can hardly be regarded as materially affecting health. Sewer-air also contains organic matter in the form of vapor, and of definite particles; but doubts have been expressed as to whether these organic particles succeed in making their way through watertraps, and some carefully executed experiments of Dr. Neil Carmichael, of Glasgow, have gone far to show that they do not do so.

FIG. 1.

There are other ways, however, in which danger comes about. The water in traps is apt to be sucked out by siphon-action, as the

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. Russell'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 twentythree 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.

In the course of my investigations I entered a wash-house belonging to one group of the houses in question. I was followed in by its owner, an old lady, who sought at once to satisfy my curiosity by assuring me that the building was rarely used; indeed, that the last time it was used was six weeks ago, at which date she had washed some linen there for a young man who had been very ill, and who lived some distance away. I had before this noticed that all the cottages were provided with sinks in their living-rooms, and that by means of these sink-pipes, which were in unbroken communication with a drain outside, offensive effluvia at times made their way into the dwellings, these having been especially noticed toward evening, when the houses were shut up and the fires were lighted. It at once occurred to me that if the sick man referred to had suffered from enteric fever, and if the drains for the several parts of the square all communicated

with the sewer by which the liquid refuse from the wash-house was conveyed away, then a specifically contaminated sewer-air had replaced the ordinary foul effluvia, and that in this way infection had been "laid on " to the several households. I found that the young man