# Popular Science Monthly/Volume 24/November 1883/Inlets for Infection

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* 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 ​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 bell-shaped 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 ​contaminating air is not so much due to occasional and temporary failure in the efficacy of the trap as to an almost constant absorption of sewer-air 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:
| GAS. | Sp. gr. | Source. | Test. | Time for reaction to show. |
| Ammonia. | ·50 | Solution. | Litmus. | 15 minutes. |
| " | ·50 | " | Nessler | 30 minutes. Ate through a small wire in less than 24 hours |
| Sulphurous acid. | 2·25 | " | Litmus | 1 hour. |
| Sulphuretted hydrogen. | 1·25 | " | Lead paper. | 3 to 4 hours. |
| Chlorine | 2·50 | " | Iodide of starch paper. | 4 hours. |
| " | 2·50 | " | Litmus-water in trap. | Began to show in a few minutes. In half an hour the whole was bleached. |
| Carbonic acid. | 1·50 | Generated. | Lime-water in trap. | 1½ hour. |
| " | 1·50 | " | Litmus suspended over water in trap. | 3 hours. |
It was, however, urged that the results would probably be different if the trap were ventilated. A ventilating-shaft (c) was, therefore,Fig. 1. 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 water-traps, and some carefully executed experiments of Dr. Neil Carmichael, of Glasgow, have gone far to show that they do not do so.
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. 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.
​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
Fig. 2.
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 ​had indeed suffered from enteric fever, and, laborers having laid bare the drains, these were all seen to communicate with the sewer above mentioned, this being further of such faulty construction as to be little better than an elongated cesspool.
In view of the danger of direct communication between a sewer and our dwellings, "What," you may fairly ask, "is the remedy?" I answer that the remedy is simply breaking the direct connection which has been referred to. In the case of a waste-pipe from a sink, the pipe should be brought through the wall into the outer air, and there be cut off, its contents flowing to a trapped drain-inlet outside the dwelling. (This point was explained by means of diagrams.) This principle of disconnection is, however, of much wider application than I have as yet indicated. All waste-pipes coming from lavatories, baths, water-closets, etc., as also the overflow-pipes from cisterns, and the rain-pipes, especially such as have their heads anywhere near windows, or beneath overhanging eaves, should, like the sink-pipes, have an air-space intervening between them and the drain-inlets into which they empty.
There is exceptional danger in the direct connection which is often maintained between houses and the sewers by means of the overflow-pipes of cisterns. These pipes are very generally provided with a "siphon-bend," but the water constituting the trapping is often absent. The ball-cock of the cistern is intentionally so contrived as to prevent overflow, and hence, when once evaporation of the water in the trap has taken place, sewer-air passes through it without let or hindrance.
Adapting the principle of disconnection to the house-drain itself, I would further urge that an air-break should always be contrived between the end of the drain and a trapped inlet leading to the public sewer; the more so as when this is effected a further safe-guard can be insured, namely, two ventilating apertures to the drain, and the maintenance of a constant current of air through its entire length.
(The conveying of infection by means of an "intermittent water-supply" was next described.)
I feel sure that many other methods by which water can act as a vehicle for conveying infection will occur to you. Milk, also, must be regarded as at least an equally important medium for the transmission of infection. I shall, however, ask your further consideration only of certain distributions of ice and cream as forming channels by which disease may be conveyed to households.
I believe that the first instance in which the consumption of ice was shown to have been followed by an outbreak of disease is that recorded in the "Seventh Annual Report of the State Board of Health of Massachusetts." The occurrence took place in one of the large hotels at Rye Beach, New Hampshire. At the beginning of the season ​of 1875 about a thousand visitors were assembled at Rye Beach, and a considerable number were attacked with a series of symptoms which led to the suspicion that they had consumed some noxious article. The incidence of the disease was entirely confined to three hundred persons occupying one of the large hotels. The sanitary state of this hotel is said to have been exceptionally good, and, although suspicion seemed at first to attach to the water-supply, yet the disease was found to have affected many who, "having apprehended trouble from the use of the water," which was strongly impregnated with salts of lime and magnesia, "had carefully limited themselves since their arrival to other beverages." Indeed, as the result of a careful process of elimination, suspicion came at last to be directed to the ice furnished to the house. The water obtained by melting the ice was discolored and charged with suspended matter, and gave off a decidedly disagreeable odor; the atmosphere of the ice-house was offensive, and some persons who had used the ice away from the hotel were found to have suffered in the same way from violent illness. The ice in question had been derived from a local pond, the water of which was found to have become foul from long-continued stagnation; one portion of the pond, measuring about five hundred feet in length and one hundred and fifty feet in width, was occupied by "a homogeneous mass of putrescent matter." A piece of ice, carefully cleansed from all surface impurities, was then melted, and the water thus obtained was submitted to chemical analysis, the result being the detection in it of a quantity of "decaying organic matter." The use of the ice had also in the mean time been discontinued, and coincident with its disuse "there was observed an abrupt amelioration in the symptoms of nearly all who had hitherto been ill." So, also, no fresh attacks occurred during the remainder of the season.
Even among the more educated classes there prevails an impression that even if water is contaminated it is purified by freezing. Many experiments have, however, shown the fallacy of this view. In some of these made recently by Mr. C. P. Pengra, an American chemist, various organic matters (urea, albumen, etc.) were mixed with water, and the specimens were gradually frozen. A certain amount of purification did take place—the ice containing thirty and even forty per cent less organic matter than the unfrozen liquid. But a large amount of the added pollution remained, and the investigator, though expressing surprise that the purification had been as great as it was, says that the experiments afford abundant proof that we ought not to tolerate the indiscriminate collection of ice.
These experiments do not, however, prove that the contagium of an infectious fever can withstand the process of freezing, but as to this we are not left in doubt. Dr. E. Klein, F. R. S., thus reports the results of some of his experiments in freezing bacillus anthracis: "I have exposed in a capillary pipette fluid full of spores to the influence ​of ether spray, and, having thus kept the liquid frozen for several minutes, have injected it into the Guinea-pig and rabbit with fatal result. . . . I then placed a capillary tube filled with spores in a mixture of ice and salt, and kept it there for one hour exposed to a temperature of 12° to 15° Cent, below freezing-point; after thawing, the material was injected into the subcutaneous tissue of a Guinea-pig. This animal died of typical anthrax on the third day."
We are thus bound to accept the position that the morbific organisms, the introduction of which into the human system produces specific infectious diseases, are not destroyed by freezing, but, on the contrary, that ice collected from an infected water and supplied to households would act as a vehicle for the introduction of the poison of those diseases. In short, a wholesome ice can be derived only from a wholesome water.
I now pass to my last point. On the 9th of June, 1875, a party of sixteen persons sat down to dinner at a house in South Kensington, and later on in the evening about one hundred and fifty additional guests assembled with the family of the host and hostess in the drawing-room; the service of the house was also re-enforced for the evening by seven extra servants. Within five days eighteen of the assembled guests suffered from more or less well-marked attacks of scarlet fever; two others had "sore throats"; one of the waiters had scarlet fever; and a few days later a lady, not at the house on the 9th, but who lunched there the next day, was found to be suffering from a distinct attack of the disease. In all, twenty-two persons were attacked.
The circumstances of the outbreak were investigated by Dr. Buchanan, F. R. S., and his report on it is specially instructive as indicating the method in which such an inquiry should be conducted. It was ascertained that the scarlet fever could not have been communicated by any of the guests, by any member of the host's family, nor by any of the servants, nor indeed did the circumstances of the outbreak suggest infection from such a source. On the other hand, strong circumstantial evidence was forthcoming in favor of the infection having been communicated by means of some article of food or drink.
The dinner guests were the principal ones affected; several of the household who could not have touched any of the articles of food served up escaped altogether, and there was a marked incidence of the disease on those who had several opportunities of eating certain exceptional articles supplied on that day. Up to this point, however, no one article of food had come under suspicion.
Two special supplies of cream were delivered at the house on the day of the entertainment; one, which arrived at 4 p. m., was "double cream" from a London dairy, and was used for ice-puddings, custards, and "creams"; the other, arriving at 5 p. p., was from a Hampshire dairy, and was mainly used as cream. The latter supply was generally ​used by all the evening guests, among whom there was but little scarlet fever; the former, or four-o'clock, cream was distributed essentially to the family and to the dinner guests. It was again used at luncheon the next day, and thirteen persons who were known to have had opportunity of partaking of it suffered from scarlet fever within five days. The bulk of this four-o'clock cream was used in the preparation of articles which had to be boiled previous to their being used in a cool or frozen form, and those persons who partook of such articles alone were not specially attacked. But of this cream some that was in excess of the cook's requirements was put into at least one jug along with the five-o'clock cream.
This mingling of the two creams added materially to the difficulty of the investigation, because it was that remnant of the four-o'clock cream which had not been boiled previous to use to which interest was now found specially to attach. For "no less than seven ladies who were at the dinner, and who took cream in their coffee in the drawing-room, afterward became ill, none of them who took that cream having escaped." There was, however, no such incidence of disease on the gentlemen who took coffee down-stairs. And further, whereas all who partook of cream on the day following the dinner were ill, none of those who did not partake of it suffered. Now, it was known that it was the four-o'clock cream that was used at the luncheon on the 10th, and if it so happened that the cream which was sent up into the drawing-room with coffee for the ladies who had left the dinner-table was the jug of mingled cream, then that four-o'clock supply from the London dairy comes strongly under suspicion.
The complicated nature of the conditions which had to be contended with in pursuing such an investigation in the metropolis forbade any conclusive demonstration as to the exact method by which this special cream-supply may have become infected. It was, however, ascertained that upon one section of the London dairyman's customers there had been a large incidence of scarlet fever, and a suspicious history as to scarlet fever in the person of one of the dairy-staff who was engaged in milking and carrying out the milk was also elicited. In short, there is little doubt that the cream supplied from this dairy was the vehicle by which the infection of scarlet fever was conveyed to that household in South Kensington.
Some years ago I conducted a somewhat similar inquiry. The same disease had attacked a large proportion of persons who had met at a London dinner-table, and the source of infection must have been some article of food. In this case, fruit as well as cream came under suspicion, and the employment as strawberry-gatherers of persons in the desquamative stage of scarlet fever seemed as likely a source of infection as that which might have operated through the agency of a dairy. The circumstances were, however, too complex to be unraveled, and further inquiry was abandoned.
​In considering each of the previous channels of infection I have pointed to some remedy. That which promises most in dealing with infection conveyed in the manner just indicated is the early isolation of persons suffering from the several infectious fevers.