Popular Science Monthly/Volume 20/February 1882/Sanitary Relations of the Soil II
|SANITARY RELATIONS OF THE SOIL.
By Dr. MAX VON PETTENKOFER.
WATER plays quite as important a part in the soil as air. Obviously, no organic life, no organic change, can be conceived of without water; and we ourselves consist three parts in four of water. Therefore it may be inferred that change in the moisture of the soil must have a certain influence on its organic and organized constituents, and on the organic life within it. Two degrees of moisture in the soil may be especially distinguished: one in which air and water both occupy the pores, and one in which the pores are quite filled with water excluding the air. In the former case we may speak of soilmoisture (Bodenfeuchtigkeit), in the latter of ground-water (Grundwasser). In many cases, but not universally, the transition from soilmoisture to ground-water is very plainly indicated.
The coincidence of the existence of ground-water with the prevalence of typhoid has been a constantly recognized fact since 1856. It was discovered by Buhl, has been tested by Seidel according to the law of probabilities, and has been followed out and confirmed down to the present day by Port for the garrison at Munich, and by Ziemssen for the avenues of the civil hospitals; by whom it is shown that, when the amount of ground-water is above the average, fewer, when it is below the average, more, cases of typhus appear. The same law was discovered by Virchow for the fluctuations of typhus in Berlin. The lowest degree of saturation exists in Berlin during the later summer and the fall, in Munich during the winter, and the seasons of typhus are correspondingly different in the two cities: the latter part of summer and the fall in Berlin, winter in Munich. When the summer is unusually dry at Munich, summer epidemics prevail there also.
That the cause of these conditions is not the ground-water in and of itself, but the moisture in the overlying strata and the processes dependent upon it, is very plainly shown by two facts: first, that some typhus-centers have a porous soil but no ground-water; and, second, that the level of the ground-water may be raised and depressed by artificial means, as by damming, pumping, or draining, without any notable influence being produced upon the prevalence of typhus. The first case occurs in places where on account of the steepness of the descent, or of any other cause, no ground-water collects on the lower impervious strata; the second case, where the level of the groundwater is within the mark of the flood-height of a river. In Munich, for example, it was necessary on one occasion, in order to carry on some excavations in a part of the city near the Isar, to leave a gate in the river open for several months, so that the water sunk more than a metre. No increase of typhus was observed; and when the gate was closed, and the water was allowed to rise again to its original height, the typhus did not diminish. A coincidence with the prevalence of typhus appears only when the variations in the level of the ground-water proceed from the saturation or the drying-up of the strata lying above it. I have always regarded the state of the groundwater only as the best and plainly visible sign or index of the rhythm of the soil-moisture in the overlying strata.
Macpherson, Lewis, and Cunningham have shown beyond a doubt that the cholera fluctuates in its home in India, like abdominal typhus with us, inversely with the annual amount of rain and of saturation of the soil. It behaves in the same way with us. The remarkable division of the cholera into a summer and a winter epidemic, which was observed in Munich in 1873 and 1874, can be explained only by reference to the conditions of the soil as to moisture. The epidemic began at the end of an abnormally dry July, prevailed with extraordinary violence till the beginning of August, became stationary about two weeks afterward, and seemed wholly to have disappeared at the end of October, only to break out anew with greater violence in November after a long spell of dry weather, and continued till the end of April, 1874. The city of Augsburg, nine miles from Munich, suffered more severely in proportion than that city in 1874, but was quite free from cholera in 1873, notwithstanding many cases were introduced. It had thirty per cent more rain in that year than Munich.
I can not go further into the consideration of these circumstances; I only cite them as evidence of the influence of moisture in the soil so far as it is measurable by the proportion of ground-water present. We are more nearly concerned with the relation of the soil to the water which we apply to our own use, which we draw from wells and springs, to water as a vehicle conveying matters out from the soil. When typhus or cholera rages epidemically in any place, two parties immediately set up a contention as to whether the epidemic influence proceeds from the water or the air. It must be admitted henceforth that either is possible, that a so-called sickly soil can impart its noxious properties equally to the water and to the air it contains, but it may also be that only one of these ways is possible as to certain matters and lower organisms. Observation and experiment must decide upon that. Most physicians have hitherto considered that infection was probably most directly conveyed through the water, and the so-called drinking-water theory has been developed from this view. It has, however, been ascertained that the best known infectious agent in the soil, the Bacillus malariæ, which Klebs and Tommasi-Crudelli have discovered and studied in the Roman fever-districts, can not live without air. These investigators found that the malarial poison was not communicated to the water that stood over a richly malarious mud. Tommasi says, in his latest work on the Roman malaria and the ancient drainage of the Roman hills, that "the Bacillus malariæ is preeminently an air-living organism." Among the conditions favorable to its propagation in a malarial soil—which need not be a swamp-soil—Tommasi specifies a temperature of about 20° C. (68° Fahr.), a moderate degree of steady moisture, and the direct action of the oxygen of the air on all parts of the mass. He says further, "The lack of one of these conditions is enough to cause a suspension of the development of the spores and of the increase of the malarial ferment." If any one, however, believes that this organism must also remain inoperative when it passes into our blood because that is a fluid, he should be reminded that it makes a great difference whether we put such organism, taken from their airy nests in a moist soil, into cold water, or into warm blood where air is supplied to them from the corpuscles.
We can not, indeed, answer, with the results of experiment and microscopical investigation, questions respecting the infectious diseases with the specific germs of which we are not acquainted, but we may be guided in the matter by other facts. Naegelli says: "Contagion fungi can keep up their peculiar activity in water only for a short time. The purer it is the less food they find in it; they are very soon removed by exhaustion in clear spring-water; and, even in water that contains food for them and where they can multiply fast, degeneration quickly sets in, and they are changed into common ferments."
Inasmuch as we are not acquainted with the germs of typhus and cholera except through their infectious operation, we can not, so long as we use at the same time the air and the water of the infected place, decide whether the epidemic germ is imparted to us by the water or by the air. If only one of the elements could be used while the other could be entirely excluded, we might anticipate a time when investigation should bring us to a decision on the subject. Many cases are now known where cholera and typhus have run their course without any part of the local water having been used as drinking-water, but not a single case where the local air was excluded while the local water was used. A severe epidemic of typhus that prevailed in the city of Basle last fall and winter enforced the lesson that not even the purest water, brought from far away in the Jura, could afford protection against those diseases. With this fact the probability, in cases where the epidemic influence can be ascribed to both the air and the water, that it exists in the water, falls to a minimum. We may then ask, Why might not the infection in these cases have been brought out from the soil by the air? It is not my intention to argue here, where discussion is not possible, against the drinking-water theory; I only call attention to the fact that the most convincing proof of it is wanting. My disbelief in it, however, does not prevent my desiring pure and abundant water for all dwelling-places of man, for we need it, not only as a means of protection against typhus and cholera, but for the daily use of sick and well; not only for the sake of cleanliness and for food, but also as a luxury.
The examination of the fungoids has brought out many facts of great hygienic importance, among them some that concern organic life in the soil. I acknowledge the fact gratefully, but can not abstain from indicating a few points which show the necessity of being guarded in practical hygiene against too hasty conclusions. Mycology would assume more than belongs to it, if it should imagine that hygiene was first placed on a scientific foundation or that it first reached a scientific standing when the cultivation of bacteria was begun, or that it had nothing more to do in the future than to look into the microscope and work with the steaming-pot and wadding-stopper. The professional hygienist has still much else to do; but if he keeps himself familiar with the results of the investigation of the germs, then we may have another hygienist who shall make as beneficial a use of them as the surgeon Lister has made of the investigations of Pasteur and others in his antiseptic bandage. The mycologist did not deduce the ultimate practical results—that belonged to the surgeon; and on this ground I believe that the hygienist is not yet a superfluous piece of furniture.
The mycologists have told us, for example, that particular solutions and concentrations of the same are essential for certain ferments or certain of their properties, and that they thrive weakly or not at all in fluids otherwise constituted. A fluid may contain all the necessary constituents, but be too diluted or too concentrated. We may consider all putrefaction and decay of suitable substances, the refuse of our households, the waste water with which we irrigate and manure the soil, as affording food-fluids for the lower organisms. Then we might think—and the like has been thought and said—that dirt is not dangerous to health if it is only properly concentrated. It has been asserted that there is much more dirt in the country and in the villages where citizens go—as they say—to get the air, than in the city. A closer investigation would, however, show that there is a real difference between the city and the village, between country life and city life, but not between the consequences of filth in the city and in the country. Cleanly kept houses are healthier than dirty ones, even in the country. The villages, however, are only apparently filthier than the cities. Indeed, the great density of the population of the cities is in itself like a concentration of the filth, and the scattering of the dwellings in the country is like a dilution of it. In the villages the manure-heaps are on top of the ground and open to the air, which, ventilating them freely, effects a salutary dilution and change: in the cities we do not bring the dirt out into the yard, but we deposit it by the walls of our houses; we do not let the free atmosphere work upon it, but try to keep it away from the air as much as possible by inclosing it in pits which are well covered and arched over, but are connected with the house by invisible pipes and canals. We let nothing escape into the free air, but believe that we Heed not regard what reaches the ground under the house and the air within the house. In the cities we insist very much on outward cleanliness, that the dirt must not be exposed, and cover it up beautifully in our houses and yards, so as to make the impression that there is none, as a dirty skin and foul linen may be covered by handsome outer garments.
Admitting that there may be a kind or amount of concentration of filth in the soil that will prevent the growth of certain ferments, as the development of fermenting bacteria and fungoids is prevented in fruits by seething them in concentrated sirups, hygiene has yet to ascertain how highly concentrated filth in the soil must be to prevent the ferments in it that contribute to cholera and typhus from being effective. It should also be borne in mind that even if a sufficiently high degree were reached at any place on the premises, as, for example, in a cesspool, that concentration would cease and a favorable degree of dilution would take its place, somewhere in the neighborhood, at a greater or less distance from the focus of filth. We should therefore always insist upon the degree of cleanliness which we understand to promote the greatest possible prevention and dilution of filth, as our hygienic aim; and we shall furthermore do well, if we remove not only from our houses, but from the neighborhood, and keep removed, all that seems to us to be dirt, and offends our innate æsthetic feelings.
The mycologists have further taught us that no germs escape from fluids and moist objects by mere evaporation, but that they only pass into the air in the form of dust, or when gases are generated and puff out, or when something adheres to things that are washed with such moist objects. We might be tempted to conclude from this that nothing more is necessary, to make and keep our abodes free from disease, than to keep everything properly moist. But, aside from the fact that damp houses and damp soils are positively disadvantageous to health, it would not be possible to maintain such a degree of moisture or other conditions that it should never be too dry, that there should never be any spurts of gas, and that no germs should ever be washed off. We can judge of the uselessness of such efforts from the fact that no one has ever found air, either out-of-doors when it has rained incessantly for a long time, nor in a house where it is still moist, that was free from mold. We attach more importance to the fact, likewise established by mycologists, that all germs flourish only in fluids and damp media, and that moist walls, not dry ones, become moldy.
If moisture really afforded protection against the escape of germs, we might imagine the drains and sink-holes connected with our houses to furnish the best kind of drainage, because they are always moist, and contribute something to the required moisture in the soil. I consider these sinks close to the house to be dangerous neighbors, even when they are designed only to carry off rain-water. I proceed upon the time-honored experience of physicians that certain malarious diseases prevail most actively in damp spots in houses and villages situated in hollow places or at the foot of slopes, after inundations. A sink is an artificial trough, an artificial flood-region for each house, into which is concentrated the drainage from the roof and from the surrounding ground. By it a certain part of the house-ground is exposed to occasional floods, which can have no other results for the house than the occasional inundations in a larger region have for the places lying within it. When such pits are unavoidable, it is well to have them as far as possible from the house; but it would be better to conduct the water coming from the roof or elsewhere to some place where it can no longer prejudice our health. I look upon the removal or great diminution of these sinks as constituting the chief advantage of the sewerage of cities. The hygienic value of sewerage may have been sometimes exaggerated—there was a time when many believed that it would remove all sickness, and it would not be surprising if the reaction against this exaggeration should lead to an undue depreciation—but it is an established fact that every city that has completed a well flushed system of sewerage in connection with house-drainage has gained in health, and that its death-rate, especially from diseases connected with the soil, has diminished. I mention the reports, on the frequency of typhus before and after sewerage, of John Simon for the English cities, of Varrentrapp for Frankfort-on-the-Main, and of Lievin for Dantzic. We hear, indeed, that the general prevalence of typhus has ceased, and that its disappearance in these cities is wrongly placed to the credit of costly sanitary works; but the coincidence must be full of significance to every unprejudiced person that the disappearance of typhus in different cities has not taken place simultaneously and in the same degree, but has generally begun with the introduction of water-works and sewers. In Hamburg, for instance, improvement began to be evident in 1848, and in Dantzic in 1872. If now we conclude that the genius epidemicus has undergone a change, this genius must have manifested a wicked partiality for Hamburg and a devilish maliciousness toward Dantzic, to have kept the latter city so long in his claws. Soyka recently communicated to the meeting of the German Sanitary Union a statistical report respecting the typhus in Munich, in which the influence of sewerage was set forth in the plainest manner, perhaps more plainly than it has been done in any other case. It is known by long experience in this city that abdominal typhus, when it is epidemic, prefers certain quarters, including sewered and unsewered parts alike, and that it spares certain quarters, including sewered and unsewered parts alike; showing that the disease is generally connected with the local situation, not with the existence or nonexistence of sewers. Now, Soyka has found that between 1866 and 1880 typhus diminished in the unsewered and the old and badly sewered parts of the city, in round numbers, only ten per cent, in the favorably situated and well-sewered parts about twenty per cent, in the unfavorably situated but well-sewered parts about forty per cent'. That the wonderful result in the last case was accomplished by sewerage becomes obvious when it is considered that in it an otherwise fertile typhus-field, in which more seed was to be destroyed, had to be dealt with. Such facts make it very hard for the opponents of sewerage to continue to deny its hygienic advantages.
A well-regulated system of sewerage with adequate flushing not only promotes the removal of much filth, but also effects a great dilution of all soluble and floating dirt, and contributes toward rendering it harmless and effecting its complete destruction. The opponents of sewerage insist that it is impossible to construct a perfectly tight system of sewers. This is not essential; it is enough to reduce the quantity of impurities penetrating into the soil, so far as they are of an organic nature, to so low a degree that they shall he quickly changed and rendered harmless by the soil. The ground has a certain power to purify itself.
Falck made the discovery not long ago that water containing infectious matter, formed and unformed ferments, organic poisons, etc., ran off pure after having been filtered through very thin beds of sand. At first, the ground only absorbs, as, for example, finely pulverized coal removes matters from fluids; but Soyka has found that under conditions of sufficient dilution and exposure to air a real destruction of the absorbed organic matter also takes place, so that even substances that are otherwise unchangeable, as, for instance, strychnine, are as completely destroyed by it as if they had been burned in the fire. This explains why the soils of many places that have been inhabited from the earliest times so frequently look to the naked eye, when they are dug over, like virgin soils. Traces of impurity are visible only in places where more is demanded of the ground than it can perform. It is therefore not surprising that the ground under the sewers of Hamburg does not appear to have been contaminated to any great extent. Wolffhügel's investigations, on the other hand, show that the ground under cesspools and drains, in which filth accumulates in a more concentrated form than in flushed sewers, presents a very different appearance. Professor Hofmann's most recent investigations in the soil of the streets of Leipsic show that the ground under the bottom of even badly built sewers is much cleaner than that over their tops or that under the pavements.
Very instructive are the researches of Emmerich, showing that various kinds of foul water, which are sure to kill when injected under the skin of rabbits, become harmless as soon as they are shaken up with common sand, or if they are diluted with a certain proportion of pure water.
Every foul soil which we. cease to pollute purifies itself again in the course of time, and every clean soil, to which no more impurity is introduced than it can work up, remains clean. It is certainly interesting that this purification of the ground is dependent for the most part on the activity of the lowest organisms, as has been proved with reference to the conversion of nitrogenous organic matters in the ground into nitric salts, or to what is called nitrification, by the researches of Schlösing and Müntz. We know as little of the nitrifying germ in the ground as we do of the cholera and typhus germs, but we can and must judge of it by its works. We learn from its operations that the representatives of the lowest organic life, of the cell-life, perform not merely injurious but also very useful functions, that they are not merely noxious or poisonous plants; and we need not be surprised if a later age, when more has been learned in these matters than is now known, shall cultivate the useful bacteria, and make war only upon the injurious ones.
As there are soils which are more easily nitrified than others, so there are those which more readily bring forth disease than others; and it is the duty of hygiene to search further into the biological processes going on in the ground. We are still very far from the end: a boundless sea of probabilities lies before us; but that need not prevent our weighing anchor and spreading sail.
Hitherto we have allowed ourselves to be guided in hygienic practice and technics predominantly by the feelings, instincts, and what we call common sense, and have only very recently begun to establish our practice, which is, indeed, very primitive, on a scientific and experimental footing. Dirt and impurity have till now been somewhat indefinite conceptions. We use the terms whenever our innate or cultivated sense of cleanliness is unpleasantly affected; they are generally called out by impressions on our sense of smell, taste, or sight. What we call cleanliness plays an important part in daily life, in a similar manner to that which conscience, the sense of right and wrong, partly innate, partly inculcated, plays in our moral life. Just as it can be regarded as a fact that conscientious men as a rule accomplish more and better than unconscientious, so cleanly men as a rule are healthier and live longer than uncleanly men. As conscience is more or less developed in different degrees of human civilization, so also is the sense of cleanliness. Under the guidance of analogous feelings, we have instinctively and empirically found out what it is to our advantage to eat and drink, and how we should clothe ourselves, before these subjects could be dealt with scientifically.
Our established hygiene also was probably based in the first instance chiefly on the suggestions of feeling. Those who are moving in the new scientific direction should guard against considering all that is not scientifically confirmed as wrong and unfounded, but they should also not hesitate to subject established rules to a thorough scientific and experimental criticism. This will necessarily teach us that mere feeling has dictated much to us that rests upon false suppositions, and can either be omitted or must be changed. Practice or technics always precedes science. Our branches of trade and industry also began on empiric roads, and were carried on in them for thousands of years; but how greatly have they been changed, improved, and simplified, and how many new branches have arisen since we began to apply the sciences of physics, chemistry, and mechanics to them!
Hygiene, or the science of health, has a widely extended field of labor in laying a scientific foundation for our sanitary regimen. Even if in many cases it only shows that all is not as it has heretofore been supposed to be, that has its great practical value. What harm did it do to medical practice that the Vienna medical school in its day showed up the errors of the then prevailing views, and radically assailed the practice founded upon them which had been adopted for centuries? An analogous example in contemporary hygiene was afforded at the meeting of the German Public Health Association, when Hofmann and Siegel showed by the light of experimental researches and exact observations that our church-yards and burial-grounds, provided the soil is in a proper condition, and a proper, easily applied restorative treatment is adopted, are not so detrimental to the ground-water and air, and consequently to the health of persons living near them, as has been heretofore believed, but that the water from wells inside of the church-yards is generally purer than that in the inhabited places around them, so that in this respect we have more to fear from the living than from the dead. We are injured by our method of burial quite as little as we were injured when systematic blood-letting in inflammatory diseases was abandoned in consequence of the observations of Skoda and Rokitansky.
It will not be otherwise with hygienic practice than it has been with therapeutics, if we now begin to apply a scientific method to it. May the medical faculties and the government speedily grant means to do it! The most beneficial practical results will not fail to be realized.
- An address delivered before the Association of German Naturalists and Physicians, at Salzburg, September 18, 1881.