Popular Science Monthly/Volume 60/January 1902/The End of the Filth Theory of Disease


FOR half a century in this country, and for a longer time in England, the filth theory of disease has dominated medical thought and has been accepted with trusting faith by the public, particularly by the better educated portion thereof. The idea that filth is the cause of disease dates back to a much earlier period. It has probably been a common belief among most civilized peoples. In colonial times many of our physicians believed in the close connection between filth and disease, and these notions sometimes found expression in laws. The prevalence of yellow fever in most of our seaboard cities during the last years of the eighteenth century did much to advance the filth theory, for this fever was held by many physicians to be par excellence a filth disease. The popular ideas were doubtless illustrated by the legislation enacted in Massachusetts, which provided for the summary removal of 'any nuisance, source of filth or cause of sickness.' This law has since been copied by fourteen states. The filth theory, however, did not become the vogue until the latter half of the nineteenth century. Its great popularity was largely due to the efforts of three men: Chadwick in England, Pettenkoffer in Germany and Shattuck in the United States, but doubtless most of all to Chadwick. Edwin Chadwick was a lawyer and social reformer. He was intensely humanitarian, and the misery then existent in England appealed most strongly to him. He saw that the poor people were filthy and sick, and he assumed that the sickness was due to the filth. There were some who objected that the relationship was not proved, but their objections amounted to little at a time when scientific reasoning was just beginning to find a place in medical thought. The practical reforms brought about by Chadwick and his followers in improved housing for the poor, improved refuse disposal, the introduction of drainage systems and the betterment of water supplies, certainly resulted in increased comfort, and constituted a decided advance in what we call 'civilization.' But they did not exterminate the infectious diseases as had been hoped and promised. The filth theory found strong supporters among engineers, and later among drain-layers and plumbers. These men accepted honestly enough the teaching of their medical advisers, and naturally became active propagandists of a theory which demanded such services as they alone could render.

From the middle until nearly the close of the nineteenth century, the germ theory, during the period when it was little else than a theory, furnished many arguments for those who contended that filth was a fertile source of disease. Putrefaction and fermentation were known to be similar processes, and were believed to be due to the vital activity of minute organisms. There were good grounds for believing that diseases of an infectious nature were also dependent on the growth in the body of similar 'germs,' and this theory from 1850 grew rapidly into favor. The germ theory led Dr. Farr, Registrar General of England, to classify most of the infectious diseases as 'zymotic' or fermentative diseases, for the disease poison was supposed to act, as in truth it does, as a ferment in the blood or other tissues in the body. If both putrefaction and disease were due to the action of minute organisms, what more reasonable than to believe, said the theorists, that putrefying material harbored and developed the 'germs' of disease?

The filth theory then, which has had such a powerful influence on the public mind, assumed that most of the infectious diseases were directly and specifically caused by germs or other more subtle emanations from decaying animal or vegetable matter.

Furthermore, it was claimed that while such emanations might not in every case produce a specific disease, they did tend almost always to affect injuriously the general health, and lower the vitality of persons habitually exposed. Hence the sewer gas theory which has found such acceptance, and which has taught that the gas formed from the filth in drains is so injurious to human life that portions so minute as not to be appreciated by the senses are yet harmful in the extreme. It was taught by medical men and health officials that filth and decay in every form were a serious menace to health, both from the disease germs which they contain, and the poisonous gases which they give off; and this teaching is received and accepted, even to-day, by a large portion of the medical profession, health officers and the public at large.

It is true that ever since this theory was promulgated some have been led to doubt its dicta, because in the first place they often found filth to abound where little zymotic disease existed, and even where the 'general health' of the people was high. On the other hand, zymotic diseases were frequently found in the cleanest of dwellings, and where the best of plumbing kept out all sewer gas. But most sanitary officials accepted the theory as fact, and acted accordingly, some used it simply as a working theory awaiting more definite knowledge, and a few were led by their experience to allow it little weight in their work.

As soon as the germ theory of disease ceased to be a mere theory, and the true facts in regard to the etiology of the infectious diseases began to be known, and bacteriology gave us exact knowledge of the life history of the minute organisms which are their cause, the erroneous generalizations of the filth theory became apparent. We can now to a large extent discriminate between filth that is dangerous and that which is not. We know that the gaseous emanations from decaying matter do not produce specific disease. We know that the germs themselves are much more rarely air borne than had been thought, and that they are not thrown off into the air from the moist surfaces of the materials where they are largely found.

Observations of cholera outbreaks, both in England and this country, furnished the best arguments for the filth theory. This disease was in a great number of instances traced to wells or streams polluted with leakage from privies or drains. The disease abounded in filthy locations and among filthy people. It was perhaps natural, though not logical, to accuse all filth as likely to produce cholera. We now know that cholera is due to the comma spirillum and that this germ is thrown off from the patient in the discharges from the bowels, but that outside the body it rarely survives a few days, and practically never increases in number. Excrement from cholera patients may infect drinking water and so cause the disease, or among the uncleanly, fecal matter may be pretty directly transferred from one to another, or food may become infected by hands soiled by fecal matter, or the germs may be carried to the food by flies or other insects.

It is not filth that causes cholera, but a particular kind of filth, namely the excrement of cholera patients. Furthermore this filth and its germs are not air borne, they are not breathed in, but taken in through the mouth. This exact knowledge does away with the vague fear of all filth as a cause of the disease, and greatly simplifies the means necessarv to control it. It is true that the filth theorists did much to prevent cholera, for in their warfare against filth they demanded a water supply from a source which could not be contaminated, and they demanded sewers to remove all excremental matter. These great public improvements make it far easier to control cholera than it was before their inception. The filth theorists were successful thus far, because, so far as cholera was concerned, there was a modicum of truth in their theory.

What has been said of cholera is applicable also to typhoid fever. This disease is due to a bacillus which does not grow outside of the body, but is carried in excremental filth just as is the cholera spirillum, and it must be controlled in just the same way.

The diphtheria bacillus is also strictly parasitic and grows, except in rare instances, on the mucous membrane of human beings. From persons so infected it is transmitted to others, usually by means of cups, spoons, pencils or other articles, or directly by kissing or fondling. Diphtheria was a few years ago considered a filth disease and was often attributed to sewer gas. We now know that the only filth to be feared is the secretions of infected persons.

Bubonic plague has always been classed as a typical filth disease, but here again careful laboratory work has resulted in a vastly clearer knowledge of its causation, though a great deal yet remains to be learned. The bacillus which causes it was discovered by Kitasato in 1894; and it has been found that it rarely if ever increases in numbers outside of the body, but rather tends to die off, frequently very rapidly. There is much reason to think that fleas and rats become infected, and are important factors in the spread of the disease, though more evidence on this point is to be desired. In any event it is shown to be a contagious disease, though perhaps not usually directly contagious, and that it does not develop in filth. We might have a perfectly drained city, with modern plumbing, efficient scavenging and the purest of water, yet, if the inhabitants were careless in their habits and opposed isolation, the disease would spread as in an undrained and poorly watered city. It might require rats and fleas to cause an epidemic; but these animals played no part in the filth theory.

Tuberculosis was never classed as a filth disease, though the introduction of sewers has been held to cause its decrease, it is claimed by draining the soil. It has, however, been proved to be a bacterial disease, but the bacillus will not grow outside of the body and has no relation to filth, except so far as matter expectorated by a consumptive is filth.

Typhus fever, smallpox, scarlet fever, measles and whooping cough have by some enthusiasts been attributed to filth, but very few observant persons who have studied the distribution of these diseases and followed their outbreaks consider them other than purely contagious. They, of course, never originate in filth or develop in filth, but may spread more among filthy people just because such persons use very little soap and water and allow their faces, hands, belongings and dwellings to become and remain smeared with mucus, saliva, pus and other infectious material.

Malaria has for centuries been considered to be the product of decaying vegetable matter, but its true relation to such material has only recently been discovered. The mosquito is the bearer of the malarial parasite, which in this case is a protozoan rather than a bacterium, and the larvæ of the particular species of mosquitoes which carry this disease live only in shallow pools where they are protected from their enemies and find an abundance of food. Water which is really filthy is not congenial to them.

Yellow fever is the one disease which it has been believed could surely be traced to filth. No disease in this country is so dreaded, and its supposed dependence upon filth has made it the last stronghold of the advocates of this theory. It has been held by almost all observers that this disease is carried in fomites, i. e., lives outside of the body, and is thus implanted in new localities, where it develops in a filthy soil, giving rise to new foci of the disease. We have been taught that by keeping a city thoroughly clean, yellow fever could be excluded as it would find no place to grow. Such methods, however, never have been and never could be successful. We all owe a great debt of gratitude to Surgeon Reed and his associates for teaching us the true method of combating this disease and dealing a death blow to the filth theory. By their experiments in which they failed to transmit the disease by fomites, they showed that the poison, the exact nature of which still remains unknown, does not live outside of the body and therefore can not develop in filth. The mosquitoes which transmit this disease do, unlike the malarial mosquitoes, often breed in filthy water, such aa cesspools, dirty gutters and the like, and this doubtless is the kernel of truth in the filth theory of its origin.

Thus one by one the zymotic diseases have been shown to be purely contagious, and not to have their origin in filth. In not a single one of these diseases has our more exact knowledge placed its source outside of man or other animals. But it may be argued that though the specific diseases may not arise from filth, we still have to fear the gaseous products of decomposition, and that the foul emanations from sewers, vaults and dung-heaps may undermine the health and pave the way for these diseases. Probably more sins have been attributed to sewer gas than anything else of this kind, but we now know that the air of modern sewers and well constructed drains is practically harmless. It is true that in confined cesspools and choked drains, injurious gases like sulphuretted hydrogen, marsh gas or carbon dioxide may be formed in such quantities as to be fatal to life, but in ordinary sewers and drains, with their facilities for ventilation and rapid motion of contents, such accumulations are impossible, and a slight leakage of sewer air, which was formerly considered so dangerous, has been shown by the chemists and bacteriologists to be harmless. Foul odors from manure piles, garbage barrels, soap works or offensive manufactories are when concentrated intensely annoying and often nauseating to those who only occasionally breathe them, but those who are constantly exposed to them do not suffer at all and do not notice them. It is also observed that plumbers and sewer cleaners are not at all affected by the odors to which they are exposed. When these odors are slight there is no reason to think that they affect the health at all, and in any event the disturbance which they cause is not lasting. The burden of proof lies with those who claim that the gases of decomposition are a serious menace to health. Most of the alleged proof relates to the production of specific diseases like typhus, typhoid and cholera which we now know can not be caused in any such way. Evidence tried by modern methods of scientific enquiry is lacking. Such evidence as we have shows that those persons who are constantly exposed to the gaseous products of decomposition do not suffer therefrom.

From whatever point of view this matter is discussed, it must not be forgotten that the advocates of the filth theory did much good, for there was a certain amount of truth in the theory. Certain kinds of filth are conveyors of specific disease, and the efforts to secure better water, to build good sewers and drains, and promptly remove excreta from dwellings were true sanitation. The providing of better houses doubtless conduces to greater personal cleanliness and tends to higher standards of living. Full credit should be given to early reformers who labored earnestly according to their knowledge, and accomplished much good and very little evil. It is only those who in the light of more accurate knowledge still hold to the crude ideas of an earlier age with whom the writer would differ.

In abandoning the filth theory we should profit by experience and not become wedded too closely to the germ theory. We do know much about bacteria and protozoa and their relation to disease, but vastly more remains to be learned, and it is much to be feared that too many seek to enter the sphere of the unknown by hasty speculation rather than by the slow path of laborious research.

Though abandoning the time honored theory which was taught him, the writer has not abandoned the fight against filth. Filth is a nuisance, and is usually an evidence of some one's carelessness of his neighbor's comfort. The state or city should certainly protect its citizens against such nuisances. Good sewerage, well swept streets, prompt scavenging, public baths, clean tenements, are all parts, desirable and essential parts, of our civilization. They would be worth what they cost even if they had no relation to health; but the proper disposal of excreta and cleanliness of person doubtless do have much to do with the prevention of the spread of many communicable diseases. Much is to be gained by promoting cleanliness, but nothing by fostering false notions of the dangers of filth.