Fig. 74.—Schoolgirl with adenoids.Fig. 74.—Schoolgirl with adenoids.
The removal of adenoids is a simple operation, lasting not over a minute, and the result of the operation is in some cases almost miraculous. The medical inspectors of the New York City schools consider the removal of adenoids as a most important part oftheir work, and groups of children are regularly taken from the schools by the principal to the clinic at the hospital, where one after another tonsils are cut off or adenoids are removed, all fright and commotion being avoided by the gift of five cents as a reward.
Eyes.
Another evidence of advancing knowledge in matters pertaining to sanitary hygiene is shown in the greater attention given to the eyes, particularly of children. Such incidental troubles as headache, sleeplessness, or biliousness are frequently due to weak or strained eyes, and in the case of school children a great deal of the alleged insubordination, backwardness, and truancy of the children is caused by their being unable to see written instructions or explanations.
It is not likely that this increased difficulty with the eyes is a new thing, but rather that both physicians and laymen are more careful as well as more expert in diagnosing the trouble. The New York State Board of Health in the fall of 1907 sent out cards for testing the eyes of school children to 446 incorporated towns. The results of using these cards in 415 schools were returned and showed clearly that nearly half the children of school age in the state had optical defects. A similar test in Massachusetts recently discovered 22 per cent of the school children with defective vision, and this knowledge in itself is an advance inasmuch as it suggests to each individual or to all parents that deficient vision is common and that good eyesight is not a thing to be assumed.
In the country it is more difficult, perhaps, to realize these deficiencies, because the constant outdoor life actsas an offset to the strain during the time when close work is required, and perhaps the distance from a competent oculist serves to postpone the time of consultation, but no greater folly can be indulged in than to suffer inflamed eyes, persistent headache, and imperfect vision, if it is possible in any way to secure the services of an oculist.
Never is it worth while to buy from a jeweler, a grocer, or a hardware store a pair of spectacles, much less to buy them from an itinerant peddler, since an oculist, with his particular apparatus, can measure the seeing ability of each eye and fit each eye with the necessary lens to restore normal vision. It is better to have no glasses than to have glasses that are wrong.
Teeth.
A curious result of the recent studies among school children with defective eyes and ears has been the discovery that bad teeth were quite as important in their relation to general health as either bad eyes or ears. One eye specialist went so far as to say that the teeth of school children should be attended to first, because thus many of the eye troubles would disappear.
As has already been pointed out, the first, step in digestion is taken in the mouth, and careful chewing is not less important than the other parts of the digestive process. If one's teeth are not adapted to chewing, if they are bunched, crowded, loose, or isolated, the appearance of the teeth is the least objectionable feature. The real importance comes from the fact that with such teeth perfect mastication is impossible. The teeth themselves harbor germs which actually infect the food and favor its putrefaction. With decayed teeth, infectious diseases find a readyentrance to the lungs, nostrils, stomach, glands, ears, nose, and membranes. At every act of swallowing, germs are carried into the stomach. Mouth breathers cannot get one breath of uncontaminated air, and dental clinics, organized and conducted in the interests of the health of school children, have been altogether too little inaugurated. The use of a toothbrush should be encouraged in children as soon as they are four years old, and its habitual use twice a day is most desirable for every one.
Only regular examination by the dentist can keep the teeth in good condition, and periodic visits at least once a year to a dentist's office, not to the kind advertised by Indians where they are willing to extract teeth without pain, free, but where a regularly qualified dentist practices, should be the habit. Armenian children, who prize and covet beautiful teeth, are taught to clean their teeth always after eating, if only an apple or a piece of bread between meals, and while probably our American customs would hardly make this possible, there is no question but that a persistent and frequent use of the toothbrush will help much in reducing dentist bills.
Sleep.
From many standpoints sleep is the most wonderful attribute of the human body. Our familiarity, from our earliest years, with sleep, closes our eyes to its strange, its awful power. We know that every human being, once in twenty-four hours, will normally close his eyes and for a certain length of time be as oblivious to things present as if already in the sleep of death. It is a common belief that sleep is nature's provision for restoring tired muscles and jaded nerves, and for building up new tissue in celland corpuscle. Excessive exertion produces a numbness and exhaustion so that the body becomes "dead tired," and sleep brings back life and elasticity. And yet some parts of the body, some muscles and some organs, do not stop work during sleep, and apparently feel no bad results for their continuous lifelong exertion. Thus, the lungs, whose muscular action is estimated at the rate of one thirtieth of a horse power, have no rest day or night, seemingly without weariness. Similarly, the heart is continually forcing blood under a pressure of about three pounds through the arteries without cessation from birth to death.
Why do the muscles of the arm and leg tire and need sleep as a restorer, while those of the heart and lungs are independent of sleep? Dr. W. H. Thomson, in his book on "Brain and Personality," finds an answer to this question in the fact that the latter do their work independently of the human consciousness, while the former are stimulated and directed by the will. He points out that fatigue comes in proportion to the intensity of the mental effort expended. A baby, to whom everything is strange, whose consciousness is absolutely zero at birth, however well developed his body, sleeps five sixths of the time because of the mental efforts needed in his simplest bodily acts. Brain work, the most absorbing task of consciousness, is always the most compelling in the matter of sleep. Not the muscles themselves but the attention, the skill, the mental effort required to direct those muscles, Dr. Thomson says, constitute the reason for sleep, a reason which, to those who labor only with their hands, must seem unutterably sad. He says that while muscle work is the commonest and the simplest, so it is alsothe most poorly paid and the most degrading, and that while brain work is ennobling and the highest type of labor, it is so difficult of attainment and produced only by such grievous toil that most of us shirk it, even while reproaching ourselves at our lack of capacity and purpose. The pathetic burden of unfulfilled possibilities, he says, is the curse of labor, and only in sleep does man have temporary oblivion through which, for a time, he forgets his work and, as it were, uses sleep as an anæsthetic for the pain of labor, to rise therefrom each morning ready to carry his burdens for another day.
Lack of sleep, to those whose brains are active, speedily brings nervous disaster, and the consciousness, from being the active superintendent of the body, becomes inert, and the body drifts like a boat without a pilot. Lack of sleep to those whose work is muscular means a numbness in the nerve cells which guide those muscles, so that they disobey the will or act unreasonably and without direction. But too much sleep, like over-indulgence in any anæsthetic, is only shirking that duty and avoiding that effort to which the higher life calls us, and the sluggard who sleeps more than the tired nerves need is allowing himself to sink deeper and deeper into a slough of despond. He forgets his toil in sleep, but it is only by active, conscious effort when awake that his work may be lifted to the higher plane where the brain is active, where work ceases to be mechanical and a burden, and where that greatest reward of personal satisfaction can be obtained.
Disease may be defined as an abnormal condition of the human body, and since there is no one condition of the human body which can be satisfactorily described as normal, there is, therefore, no exact definition of disease.
What is disease for one person because of a departure from his normal health might not be recognized as disease in another person of different normal vitality. Nor is it possible to assign any particular and special cause for disease since the condition recognized as disease is the result, usually, not of one but of a series of causes or circumstances more or less connected and linked together, and in many cases not obviously associated with the resulting disease. Thus, in records of death, it is very common to see reported pneumonia as the cause underlying and fundamental, when the cause was really typhoid fever, the patient yielding to the former disease because of the enfeebled condition due to the latter. Again, many children contract diseases like measles or whooping cough because of reduced vitality due to insufficient nourishment, lack of clothing, and neglect, and their illness is said to be due to measles or whooping cough when underproper conditions of care and attention they would not have the disease at all. The causes of disease therefore may be divided into two classes, direct and indirect. In the latter class are to be included such causes as environment, heredity, age, and occupation. In the former class are to be found such causes as the introduction of disease germs into the system; the action of poisons, whether introduced into the alimentary canal or into the lungs, and such external conditions as excessive heat and cold and accident.
Effects of dirt.
At one time it was thought that diseases could spring up in the midst of dirt, and one of the strong arguments for keeping houses clean, for removing manure piles, and cleaning up back yards, was the fear that without such care diseases might be induced in those living near by. This is possible in a certain sense, but unless the seed or germ of the disease is present in a pile of dirt there need be no fear of the disease being developed. There is, however, a probability that by the organic decay and the consequent pollution of the atmosphere the vitality, energy, and resistance of the individual in the vicinity may be weakened.
It is well known, for instance, that prisoners confined in damp dark cells lose vitality, and when released, have but little of their former physical strength. In the chapter on Ventilation, it has been shown that persons confined in a small room and breathing their own exhaled air may in time become unconscious and die, and therefore it is reasonable to believe that persons living in the immediate vicinity of decaying animal or vegetable matter will suffer a loss of vitality and will have less resistance to disease.
Blood resistance.
It is well known that there are present in the body certain agencies which act as guardians of the body against disease; that there are certain corpuscles of the blood and certain liquids circulating through the system which immediately attack and if in sufficient numbers or strength drive out the advancing enemy, so that "taking a disease" in most cases means that the activity of these resisting organisms is not forceful enough to successfully combat the germs of the disease. These agencies, whether circulating liquids or cells or corpuscles, are most active in the healthy body, and anything that tends to reduce the general health, such as exposure, overexertion, imperfect nourishment, overeating or overdrinking, or lack of sleep, tends to diminish their activity and so makes the individual more susceptible to disease.
Cell disintegration.
Although disease is caused by the attacks of germs, another and far more important cause of disease is the breaking down or overstimulation of some particular organ. This is very plainly seen in diseases involving the stomach or intestines, where habitual excesses in eating lead, sooner or later, to consequent inflammation, disease, and death. This is also true of the lungs; merely living in an atmosphere full of dust will irritate the lungs to such a degree as to cause inflammation. Cancer is presumably the result of local inflammation, although the cause of the original suppuration is unknown. Similarly, appendicitis starts from some irritating cause, resulting in inflammation and the formation of pus. In very many cases the cell-disintegration seems to be a matter of heredity.
Heredity.
Heredity, the second of the indirect causes of disease seems to be assuming less importance as it is more studied. Probably in but few cases is heredity more than a chance factor in the causation of disease. Heredity, formerly considered to be the most important cause of consumption, is now understood to have little to do with this widespread epidemic, although it is agreed that children brought up in the family with a consumptive mother and father are more likely to contract the disease than if they were segregated.
It is a providential arrangement that children inherit the tendencies of both father and mother, and that the good qualities of one parent are known to offset the bad qualities of the other; probably for this very important physiological reason marriage between near relatives, where both parents would be inclined to the same weaknesses, has always been proscribed. However, even with the characteristics of the father offsetting peculiarities of the mother, it is possible for the traits of a parent to be reproduced in children, and this applies to mental traits as well as to physical. In some families there exist tendencies toward nervous diseases, such as epilepsy and insanity, although it is not accurate to say that either disease is naturally inherited. It has been observed that a tendency to cancer, to scrofula, and to rheumatism runs in certain families, but this is hardly more than saying that in certain families, where the predisposition in this direction by one parent is not offset by the tendencies of the other parent, the physical condition of the child is such as to encourage the development of diseases.
Age and sex.
As indirect causes of disease, age and sex cannot be overlooked. It is well known, for instance, that certain diseases belong essentially to childhood, measles and scarlet fever being markedly prevalent among children under ten years of age. In fact, it has been said by experts that if measles could be kept from children under five years old, the disease would be practically stamped out, since beyond that age they are less susceptible and the course of the disease is much milder. No greater mistake can be made than in exposing children to so-called "children's diseases" because of a desire "to have it over with." Not only is such exposure foolish, since it is quite possible to escape the disease altogether if in the first few years of life it is avoided, but also inviting death, since the mortality of the disease becomes markedly less and less as the age of the patient advances.
Many of the diseases of children are due to imperfect and incomplete development; either the lungs or the stomach or some other organ is not equal to its work, and the child remains an invalid or dies. Many children die from imperfect nutrition, especially in the second summer, when teething is at its height, on account of the ignorance of the mother and on account of unsanitary surroundings. No movement is more promising in the way of prolonging the lives of children than that recently inaugurated in New York which undertakes to teach mothers, of foreign nationality in particular, how to dress, bathe, feed, and bring up their children.
Another reason why disease occurs more frequently among children is, as will be seen later, that one attack ofa disease frequently confers immunity upon the patient, so that, for example, a child having scarlet fever is not likely to have the disease later on in life; but this is no argument for exposing one's self to contagion, since it is quite possible that even the first attack may be avoided. Tuberculosis or consumption is preëminently a disease of youth, as is also typhoid fever. It is very rare for the latter disease to appear in children or in adults over forty-five, and for the former to develop until maturity.
In old age, diseases occur due to the gradual failure of the different organs to perform their normal functions. Some of these diseases are connected with the heart and the circulation, others with the liver or with the mucous membranes, so that among those advanced in life, rheumatism, gout, cancer, and diseases of the kidneys are very apt to occur.
One of the objects of sanitation is to eliminate disease due to bacteria and to prolong the normal life, so far as is possible, past the early period when diseases are easily contracted. It is not hoped that death can in any case be prevented, but hygiene will have done its utmost when death occurs only among the aged and when the diseases then causing death are only those which are consequent upon the wearing out of the body.
So far as sex is concerned, the ordinary rules of hygiene or the violation of those rules seem to have but little concern. It is generally understood that males are on the average shorter-lived, by a few months, than females, and all statistics support this position. Some diseases, like typhoid fever, attack males more than females in the ratio of three to two, while cancer attacks females to a greater extentthan males at about the same ratio reversed. Generally speaking, however, excepting in so far as their occupations and manners of living make different their vital resistance, the principles of hygiene are not affected by the incident of sex.
Occupation.
Inasmuch as this discussion is a part of rural hygiene and is assumed to apply to only one occupation, namely, that of cultivating the soil, or of raising stock, it may not be considered pertinent to discuss the effect of occupation on disease. It is worth while pointing out, however, that occupation is a very important factor as an indirect cause of disease, and that one's chances of life are vastly greater in the open country surrounded by hygienic conditions than in a city in crowded quarters, confined for long hours each day at some unhealthy occupation.
As a general warning, it may be stated that a factory containing a dust-laden atmosphere is most undesirable, and this is particularly so when the dust is mineral dust. In the country, the only comparison of conditions possible is between that of the outdoor worker and that of the indoor worker; enough has already been said upon the value of fresh air and its improving effect on the vital resistance to make further repetition unnecessary. Unfortunately, in the past the occupation known under the general term of farming has not made itself conspicuous in statistics for healthfulness; but this has been undoubtedly due not to the lack of the value of the outdoor part of the farmer's life, but to the monotony of the work and to the very bad conditions found indoors, particularly in the winter. When this indoor life has been modified so thatplenty of fresh air is supplied day and night, and when reasonable attention is paid to the demands of the body in the matter of food and drink, then the duration of life of farmers will rank high in comparison with other occupations.
Direct causes of disease.
The direct causes of disease may be due to the introduction into the human body of a specific microörganism which, if not met by the antagonistic agencies, finally pervades the whole system with its progeny or its virus. The microörganisms thus responsible for disease are commonly divided into two classes, namely, parasites and bacteria. In the first group are included those parasites that cause tapeworm, malaria, trichinosis, and hookworm; in the second group those bacteria that cause typhoid fever, cholera, erysipelas, diphtheria, and probably smallpox, measles, scarlet fever, chicken pox, and a number of others presumably similar.
Parasites as causes of disease.
The introduction of worms into the body must come either from impure drinking water, from impure food, or from the bites or stings of insects. When introduced into the body, those parasites that are inimical to man and produce abnormal conditions interfering with usual physiological functions may or may not develop further. In some cases, as in malaria, the very act of hatching the malarial brood is sufficient to throw the host on whom the brood will feed into a violent chill.
In other cases, as with the hookworm, while eggs are produced in the human body, they have no directly detrimental effect, the objectionable feature of their residencebeing due to the fact that the continual draught which they make upon the blood vessels of the intestine reduces the vitality, causing anæmia.
In other cases, as with the guinea worm, found in Africa and South America, the worm wanders from the stomach, which it enters toward the surface of the body, and finally breaks through, causing ulcers or abscesses.
In still other cases, as with that form of filaria which causes elephantiasis, the adult worm or the embryos are present in the lymphatics in such numbers as to interfere with circulation, causing the fearful swellings characteristic of the disease named.
Finally, in such cases as trichinosis and tapeworm, there is usually but little inconvenience to the human being harboring them, except when their number becomes very large. Then there may be diarrhœa, loss of appetite, and other digestive disturbances. The different tapeworms are generally responsible for nothing more than indigestion and nervousness. These latter parasites are, however, formidable in so far as their size is concerned. The mature pork tapeworm is about ten feet long, although the eggs, seen in the pork flesh, giving it its name of "measly," are only about a thousandth of an inch in diameter. The fish tapeworm, when mature, measures about twenty-five feet in length, while the beef tapeworm is about the same length. These worms can develop only in the bodies of the animals named, and find their way into the human body only through the medium of imperfectly cooked meat.
If proper precautions be taken in these directions, if only water is used for drinking which is known to be free from such parasites and their eggs, and if insects likemosquitoes and fleas are kept away by screening windows and doors, and if meat be always thoroughly cooked, the dangers of diseases from parasites will be reduced to a minimum.
Bacterial agencies.
By far the most important of the living agencies concerned with the direct production of disease are those small vegetable organisms known as bacteria. Not all bacteria, by any means, produce disease; in fact, it is not too much to say that the majority of bacteria are benefactors to the human race. Their chief agency is not to cause disease, but to prevent it, and they do this because they are able to transform the waste products of animal life, which would normally be dangerous to health, into harmless mineral residue. They are really the scavengers of the earth's surface, not actually carrying off garbage, but rather transforming it, and, in the process, not merely destroying it, but changing it so as to make it available for plant-food. It is through the agency of bacteria that the air, which is being continually overloaded with carbonic acid from the lungs of animals, is reduced and taken up by plants so that an equilibrium is maintained. Otherwise, the atmosphere would be more and more vitiated with carbonic acid and organic vapors, and every one would die as if shut up in an air-tight room. But, because of bacteria, neither is the surface of the earth overloaded with waste organic matter nor do streams, however much polluted, continue to flow without some improvement being traced in their quality.
In some of the ordinary manufacturing processes, bacteria are all-important, as in making vinegar, wines,cheese; in fact, in any of the fermented food products. In agriculture, they are entirely responsible for supplying an adequate amount of food material to growing plants. Fresh manure is not suitable for plant-food and would be of no value on the fields or in the garden except as improved and modified by bacterial action. One of the greatest discoveries of their importance recently made has to do with the way in which peas and beans are able to absorb nitrogen from the air through the agency of bacteria. One knows that plowing under a crop of peas or clover enriches the soil, and that peas or clover make the best growth for this purpose. The reason is that these plants, through the activity of bacteria, are able to absorb nitrogen from the air and afterwards to convert it into food material.
But with all these good qualities a few bacteria, gone bad, perhaps, are associated with diseases, and by a series of experiments, chiefly those of a Frenchman named Pasteur and of a German named Koch, and of their followers, it has been ascertained that certain bacteria, and those only, will cause certain diseases. These diseases, that is, these caused by bacteria, are generally spoken of as epidemic or contagious, of which typhoid fever and cholera are examples.
All contagious diseases cannot at present be definitely associated with bacteria, probably for the reason that the methods employed to find the bacteria have not been adequate. For instance, the bacteria of smallpox has never been found, although the disease is so characteristically one of bacterial origin that no one can doubt the cause. Similarly, the bacteria responsible for measles, scarletina, and whooping cough have never been discovered, although thecause of each is also presumably bacterial. More definite information on the subject of the individual and responsible bacteria will be given in the subsequent chapters dealing with specific diseases. Inquiries into the method of growth and into the life history of specific bacteria serve our present purpose only as they teach methods for the prevention of the disease. For example; when it was found that the parasite of yellow fever, in the course of its life, spent fourteen days in the mosquito's body in such a condition that the mosquito during that time was harmless, it made possible exposure to mosquitoes laden with yellow fever for a period of thirteen days from the time of the preceding case.
Antitoxins.
But the methods of combating the different diseases when once contracted in the human body, based on the knowledge obtained of the life history of these germs, have been the most important result of their biological study. A large part of this knowledge has been acquired by the study of animals which have been found susceptible and so available for experimental investigation, and it may be that the impossibility of studying measles, for instance, in animals, may be one reason why the germ has never been discovered.
There is no evidence that animals suffer spontaneously from such diseases as typhoid fever, Asiatic cholera, leprosy, yellow fever, smallpox, measles, and so on; but it seems that in animals, as in man, the disease is the direct result of the life and growth in the animal of the characteristic disease-producing germ. The fact that diphtheria or tuberculosis can be experimentally given to rabbits orguinea pigs is without doubt the chief source of our knowledge of those diseases, although, in general, it is impossible to produce diseases in any animal which will be, clinically, precisely like the disease as it appears in man. The converse of this is also true, namely, that when it has been found impossible to experimentally inoculate an animal with a disease supposed to be bacterial in nature, then but very little of that disease is known.
The most important result of bacterial studies has been the production of what are known as antitoxins, and no more wonderful discovery has ever been made. To understand as best we may the principle involved, it is necessary to explain the process of bacterial attack. When bacteria capable of producing disease are introduced into the system, either through the mouth or into the lungs or into the blood through some skin abrasion, the bacteria, finding there a congenial habitat, thrive, grow, and multiply. In some cases, this bacterial growth results only in breaking down the cell tissues at the point or in the vicinity of the place where growth occurs; for instance, if a cut is made with a dirty knife, that is, one carrying bacteria on the blade, and is not immediately washed out with an antiseptic solution, bacteria will grow and pus will form in the cut. Similarly, a splinter, if not removed and cleansed, will produce a pus-forming wound. But unless a very extensive suppuration starts, the difficulty is all local. So it is with consumption, when the bacteria are localized in the lungs and by their growth destroy the lung tissue without, at least for many weeks, affecting the general health.
There are germs, however, like typhoid fever and diphtheria, which do not produce any particular local disturbancewith the growth of bacteria, but the whole body becomes sick, the circulation of the blood is affected, and a general disturbance ensues. This is due to the action of a poison, called a toxin, which is set free as a result of the growth of the bacteria in some one part of the body, which poison is then carried by the blood throughout the entire system, inducing fever and a general debility.
Just how these toxins are formed is not certain. They are not the bacteria themselves. This we know because the disease-producing bacteria can be grown in broth and the mixture can be strained through fine porcelain, fine enough to strain out the bacteria. Yet it has been found that the clear liquid passing the porcelain filter is capable of producing disease and is a deadly poison without the presence of any bacteria at all. During the incubation period of a disease, as, for example, in the three-week period when typhoid fever is developing, these poisons are being formed and are being scattered through the body, and it is during this time that the fight takes place between these poisonous forces and the defending forces always present in the human system. As already pointed out, these defensive forces are powerful or not, according as the general health of the individual is good or bad, and we see the familiar sight of persons said to be run down taking a disease, while those not so depleted of vitality are able to resist or remain immune.
So certain are scientific men of this power and of the fact that the power resides generally in the white corpuscles of the blood that, in the presence of a dangerous infection, a person's blood may be examined, and, if the white corpuscles are not present in sufficient quantity,proper means must be taken for developing this element in the blood, or else the person must take himself away from the infection, if the infection is to be avoided.
As a result of the conflict between the toxins and the defensive forces of the body, certain vital processes are set free in the blood and in the cells which seem to possess a highly specialized power of defense against any subsequent attack. Pasteur, in his researches on the subject of rabies, developed this power of resistance by inoculating into rabbits the rabies infection of a monkey. Monkey rabies is not a severe form and is scarcely felt by the ordinary rabbit, but if the infective material (usually part of the spinal cord) of the monkey-infected rabbit is transferred to a second rabbit, the disease becomes more severe; and if the disease is passed from animal to animal, it may be built up into as severe a form as desired, up to the maximum. Pasteur found that by inoculating an individual with a one-day rabbit, that is, with the weakest brand of infection killing a rabbit in one day, and the next day with a two-day rabbit, that the person could receive this two-day inoculation without discomfort or danger because of the greater antagonism acquired by the preceding inoculation. Continuing the inoculations for fourteen days and making the strength of the infection stronger each day, at the end of the period it was found that the fourteenth inoculation, strong enough to produce the disease and kill a fresh subject, had, on account of the preceding inoculations, produced ability to withstand or counteract the actual disease developing perhaps at the same time. Fortunately, in the case of this disease, the shortest period for its development is fifteen days, and often it is a month or more afterthe bite of the dog before the disease develops. By successive inoculation of increasing strength for fourteen days, the system will have acquired a habitude to the disease which prevents the normal effects.
Diphtheria is prevented in much the same way, except that in this case horses are used, their blood being strengthened to resist the disease by successive inoculations of the diphtheria poison. It is probable that all the bacterial diseases which exert their influence through the transmission of toxins in the blood may be counteracted by the production of an antitoxin when once the method of building up this antitoxin has been learned. At present, rabies, tetanus, diphtheria, and cerebrospinal meningitis are the four diseases for which antitoxin is made commercially and generally used. For a great many years, scientists have labored without success to find an antitoxin for consumption, and within the last year extensive experiments have been made in the American army on the use of antitoxin for typhoid fever.
Natural immunity.
It may be worth noting that not all resistance to specific diseases needs to be acquired in the roundabout way just described. The state of being free from disease is known as immunity, and the way of securing immunity just described is known as artificial immunity. This artificial immunity may also be obtained in the course of events by having the disease as a child, thereby generating the antitoxin in one's own body instead of in the body of some cow or horse or rabbit.
There is, however, a natural immunity which is due to long-continued environment or to protracted heredity.The negroes in the South have, by a lifelong proximity and struggle with the disease, acquired a practical freedom from typhoid fever, although it remains with the negro sufficiently to form a focus for the spread of the disease among others not equally immune. Creoles in yellow-fever districts have a natural immunity from the hookworm disease, although probably the class are responsible for its generous transmission to the poor whites with whom they associate. Racial immunity from certain diseases may be shown by statistical studies.
Chemical poisons.
Instead of the introduction of toxins into the body by the agency of bacteria, it is quite possible for chemical poisons, not formed originally by bacteria, to be set free in the body. Sulphate of copper, for instance, is essentially a mineral poison which acts on the human system in such a way as to produce death, and certain other mineral substances may be mentioned, such as phosphorus, arsenic, and mercury, which are well-known poisons. There are also many vegetable products, not bacterial, which are poisonous in their nature, that is, distributing to the blood and lymphatics certain substances in solution which act on the cells of the various organs of the body in such a way that the activity of those organs is stopped. Opium, cocaine, alcohol, and some of the coal-tar products used for headaches, as phenacetin, are deadly poisons when a limited dose is exceeded.
There are also certain poisons engendered in the body itself whose action is similar to that of chemical bodies and which can hardly be called bacterial. These poisons represent generally stages in the process of nutrition where forsome reason the normal process is arrested and chemical bi-products are set free. Also, tissue which has been thrown off, in or by any organ, begins to decompose, thereby sending throughout the system the poisons of decomposition. Inflammation too generally results in the breaking down of the cells and the distribution of the resulting poisons. Of late years, much has been said of the poisonous property of the body waste not disposed of by excretion, and the theory of auto-intoxication, so-called, has received many adherents. The great scientist, Metchnikoff, has even gravely contended that it would be well for children to have their larger intestine removed entirely, because in that organ putrefaction occurs, the cause of the auto-intoxication he would try to prevent.
External causes.
The external causes responsible for disease are due to conditions of weather so severe as to be outside the possibility of self-protection. Excessive heat is responsible each year for deaths from sunstroke, and other conditions of weather are often the direct causes of disease, if not of death.
Accidents are the indirect cause of death, and there will always be a small proportion of the deaths occurring each year due to violence or accident. But, inasmuch as these deaths are clearly preventable, it is the duty of those interested in rural hygiene to study the reasons for accidental death, and, if the number of such accidents can be reduced, to strive for that reduction. As an example, it may be mentioned that each year a number of deaths in New York State, and probably in other states, occur from accidents at culverts and bridges, due to insufficientprotection in the way of railings and fences. A method of reducing the deaths from accidents, therefore, would include a proper survey of all the roads of a vicinity to make sure that no danger exists in this regard. Other precautions against preventable accidents will readily suggest themselves.
Inasmuch as more than 10 per cent of all deaths are due to bacterial or to various infectious diseases, it is of considerable interest to study the various means by which these germ diseases may be prevented. In this chapter it is proposed to discuss the different ways in which the active agents concerned in the spread of disease may be captured and put to death. It has already been pointed out that infectious diseases can be acquired only by the introduction of the specific germs into the human body, either through the mouth or lungs or through some skin abrasion. Further than this, it is quite as definitely known that the vitality of the germ after leaving a diseased person depends primarily upon its condition at the time of leaving the body and afterwards upon the environment which that germ finds outside of the affected person, while waiting for a chance to make its next human resting place.
It is evident, therefore, that if during the interval which elapses between the time when the germs leave a sick person and the time when they enter another person some method could be found by which these germs could be killed, the progress of the disease would be effectually stopped.
This, in the most general sense, is what is meant bydisinfection. It is a determined effort to destroy the carriers of disease while temporarily absent from the human body which is their natural home. This process of killing bacteria, however, is not so simple a matter as it might at first seem. They are, unfortunately, such minute beings that they cannot be seen, so that the warfare is waged against an invisible enemy, not, however, to be despised on that account. The methods of warfare must be uncertain, since the exact location of the enemy cannot be known, and it is manifestly impossible to disinfect the universe. What is done is to fix upon the location or surroundings where the original patient was confined, and, assuming that the germs, if any, which have escaped ready for further infection are somewhere near, to poison the air and the wall and floor of the room in question so that happily the germs may be killed.
Disinfecting agents.
The various agents used to destroy those germs which are carriers of disease may be divided into two groups, namely, heat in its various forms, and chemicals. Literally, the word "disinfection" means "doing away with infection," so that to disinfect a room is to do away with the infection present in the room. It has, however, come to have a more general meaning than this and is commonly used instead of the word "destroy," so that a disinfecting solution is the same thing as a destroying solution, applied, of course, to bacteria.
It has already been explained that by far the majority of bacteria are useful if not essential to human life, and one of the difficulties in employing disinfecting or destroying solutions is that they put an end at the same time to bothuseless and useful bacteria. As an example, the fermentation processes in the human intestines are accompanied if not produced by certain kinds of bacteria, although on occasion these harmless or useful bacteria may develop into most obnoxious germs, producing unpleasant fermentation. It might be easy enough for a doctor to make a patient swallow some antiseptic solution, like carbolic acid or corrosive sublimate or nitrate of silver, for the purpose of getting rid of certain undesirable bacteria in the intestines, but it does not need a doctor to know that for a patient to swallow such active poisons as these would not merely kill the harmful bacteria and the good ones as well, but probably the patient himself.
Antiseptics.
There is another word often used in connection with bacteria, namely, "antiseptic," and the common significance of this word applies to a substance which interferes with or retards the growth of bacteria without actually destroying them. Doctors, for instance, use antiseptic instead of disinfecting solutions on wounds, not because they do not wish to kill the pus-forming bacteria, but because the antiseptic solution will prevent their growth and not be, as a disinfecting solution, harmful to the cells which he is trying to repair. It would be folly, for example, to inject a strong 50 per cent solution of carbolic acid into a wound on the arm produced by a saw, because all the energy of the vital forces at the seat of the wound are needed for repairs, and there is none to spare for so active a detergent as carbolic acid. An antiseptic, on the other hand, is mild enough so that it does not act on the tissue at all, but merely prevents any undesirable growth of bacteria.
Deodorizers.
There are substances used, perhaps not so much around country houses as around city houses and in water-closets, which are neither disinfectants nor antiseptic, but act as deodorizers only. Such a substance, for example, may be thrown into the kitchen sink, not at all for the purpose of killing bacteria, but for disguising the smell from the cesspool into which the sink-wastes discharge. It has no disinfecting properties and is good for nothing unless the material is so scented as to be agreeable on that score. One of the frauds perpetrated on the public is the preparation and sale of the various appliances designed and regulated to produce a perpetual smell and claimed on that account to be either disinfecting or antiseptic agents. The smell is worth nothing.
Patented disinfectants.
The poison of the disinfectant or antiseptic, whether it be in liquid or in gas form, is the essence of the material, and since the value of disinfectants is based on the crude raw materials which any one can buy, it is clearly unnecessary to buy expensive patented solutions for disinfectants when ordinary lime or carbolic acid are equally as good and can be had at much lower prices.
A disinfecting solution, to be successful in its action, must be reasonably proportioned in volume to the amount of material to be disinfected, whether this be a liquid or clothing or the air of a room. It is the height of absurdity, for instance, to pretend to disinfect the air of a large room by burning a tablespoonful of sulfur on a shovel in the center of a room without even taking the trouble to close the door. It is absurd to attempt to disinfect the bedlinen in a single pailful of hot water, since even if the water was hot at the beginning, it would be so reduced in temperature by the first piece that went in that its efficacy would be lost for everything else. It is equally absurd that a liquid from a bottle, no matter how much advertised, can effectually disinfect a room, either by a gentle sprinkling of the liquid on the walls and floor or by a more thorough spraying of the air with an atomizer containing the liquid.
Disinfecting gases.
Two gases are available for use in disinfection, and these are valuable particularly in killing germs left in a room after a patient suffering from an infectious disease has been removed. The diseases referred to in the following chapters are all of this nature, and one of these two gases ought to be used in every case; otherwise the room may continue to harbor germs of the disease for months or years with the possibility of infecting a future tenant at a time when his vitality was such as to make him an easy prey. Nor must the contents of the room be overlooked.
The writer was recently told of a large family where one child had scarlet fever, recovering in September. The sick room was thoroughly disinfected, but the careful housewife, fearing damage to her blankets, had taken them to the attic before disinfection began. In the cold weather of February these blankets were brought down, and in six days the two children sleeping under them had contracted the disease.
Sulfur as a disinfectant.
When sulfur is burned, a gas is formed known as sulfurous acid, and until the last few years, it was the most common of all disinfecting agencies. The writer well remembers that when about to visit a city in South America infestedwith yellow fever, he was seriously advised to fill the inside of his shoes with sulfur as a precaution against the disease. He might as well have worn a red ribbon on his hat so far as any protection went, but it illustrates the confidence formerly shown in sulfur as a disinfectant.
It is now known that in the dry, powdered state, sulfur is of no value unless, perhaps, the germs be smothered with the sulfur flour. When burned, however, the gas given off has a certain disinfecting property, although this is limited. It has almost no power of penetrating into curtains, blankets, and upholstered furniture, although the penetration is decidedly increased if these objects are moistened either by steam or by water vapor. The proper amount of sulfur to be burned for any room is at the rate of 3 pounds per 1000 cubic feet of air space in the room. Thus, if a room be 12 feet by 15 feet and 8 feet high, containing 1440 cubic feet, it would be necessary to burn 144/100 of 3 pounds, or 4-1/3 pounds.
Before undertaking to disinfect a room with sulfur, it should be made thoroughly air-tight, and this must be done carefully, not merely by closing the larger and obvious openings, like doors and windows, but by pasting strips of paper over every crack which might allow air to escape. Thus the four edges of the window sash must be pasted up, and a strip must close the crack between the two sashes. All the doors but the one reserved for exit should be pasted up from the inside, and finally this last door pasted up on the outside. If the floor has settled away from the base-board, the cracks thus made must be pasted up. In short, the room must be made absolutely air-tight. The room should be left thus closed for at least twenty-four hours,and since there is some danger from fire, a proper provision should be made for the burning sulfur. This can be done by placing an old milk pan (a most convenient object in which to burn the sulfur) on a couple of bricks, which may be set inside a wash tub with perhaps three or four inches of water in the tub. The most convenient way of ignition is to moisten the sulfur with a little alcohol which can be readily set on fire.
Since clothes of every sort are more effectually acted upon when moist, they should be sprinkled with a hand atomizer just as the sulfur is lighted, and this should always be done in the case of any stuffed furniture or hangings. Anything that can be removed should be taken out and sterilized by steam, since live steam is the only disinfecting agent which will penetrate such things as mattresses, pillows, and rolled-up bundles of every sort, and with these last even steam is not certain. It is far safer to send a mattress to the cleaner to be steamed than to try to sterilize such bulky objects at home. It requires about twenty-four hours with the room tightly closed to generate enough gas so that the bacteria which may have found their way onto the walls or floor or ceiling or into the air of a room will be surely killed. After that time the room can be opened and then the usual household cleansing processes carried out as an additional safeguard. It is a wise measure in the case of infectious diseases, even after a room has been fumigated with sulfurous gas, to wipe off the woodwork and the walls, if their construction allows it, with a solution of carbolic acid, since in this way the germs which have accumulated on the woodwork will certainly be killed.
Formaldehyde disinfectant.
Formaldehyde is the other gas which is commonly used for disinfecting the air of a room. It is most readily produced by buying solidified formaldehyde and then decomposing it by the action of heat. Formaldehyde candles, as they are called, may be purchased at almost any drug store, and while special forms of generating stoves may be found in the open market, an ordinary heating apparatus of almost any sort will answer the purpose of decomposing the solid formaldehyde. About 20 ounces of the formalin should be used for each 1000 cubic feet of space. With this agent, however, as with sulfur, the penetrating power of the gas is not very great, and such things as mattresses and clothing should be sent to a steam sterilizer rather than be trusted solely to the power of the formaldehyde.
In using this gas, the same care about pasting up cracks and crevices in the room should be followed as already prescribed for the use of sulfur, and, as with sulfur, a reasonable precaution against fire should be taken by placing the apparatus in a tub of water or in a large pan of sand where accidents cannot happen. The room should be kept closed for at least twelve hours, and then should be thoroughly aired, and if the room is to be used again soon, the disagreeable odor may be removed by the free use of ammonia, either sprinkling it around in the room or by placing about saucers of ammonia.
Liquid disinfectants.
More common than gases and most readily suggested as disinfectants are certain liquids which have been proved both by laboratory experimentation and by actual experience to have the power of killing bacteria when broughtinto contact with them. Those liquids which have commended themselves particularly have additional advantages in not destroying fabrics, metals, or tissue with which they are brought in contact and in being purchasable at moderate prices.
There is little choice between a number of such liquids, and the number of modifications or combinations which are made and bottled and sold under some fancy name is legion. But the label, the name, and the additional price add nothing to the value of the basic chemical from which they are all compounded, and except for their convenience, they have little to recommend them.
Carbolic acid as disinfectant.
Carbolic acid is one of the most useful of these liquids, and in its various forms appears in almost all disinfectants. It may be obtained from the drug store in two forms, either as a crystal or as a concentrated solution.
A 2 per cent solution, that is, one pint of carbolic acid to six gallons of water, is the proper strength for all such uses as wiping off wooden surfaces, furniture, floors, etc. A stronger (5 per cent) solution is used when it is intended to destroy organic matter containing large quantities of germs. This is practically a saturated solution, so that if a bottle be partly filled with the crystals of carbolic acid and then completely filled with water, the water will absorb enough of the carbolic acid to make a 5 per cent solution, and the water may be poured on and off as long as the crystals remain. This 5 per cent solution is the proper strength to receive sputum from tuberculous patients, material ejected from the stomach in diphtheria, and fecal matter from typhoid and cholera patients.This strong solution should not be used on the living human body, since it is powerful enough to eat directly into the flesh, and being a violent poison, it should be kept out of the way of the household and carefully labeled to avoid accidents.
Carbolic acid has no value at all in the way of disinfecting the air, although fifty years ago surgeons were accustomed to use a spray of carbolic acid around the operating table before an operation in order to destroy any germs of the air lingering in the vicinity. It is equally futile to pour carbolic acid into sewers or to stand it around on the mantelpiece for the purpose of disinfecting a room. Nor are sheets wet in carbolic acid and hung over doorways and at the end of passages anything more than a remnant of medievalism.
Coal-tar products.
There are certain preparations made from coal-tar which, either alone or combined with carbolic acid, have very strong disinfecting properties and which are the bases of most of the patented disinfecting solutions now sold. They are commonly called cresols or creosols and a 4 per cent solution of any of the three ordinary forms will destroy bacteria in a few hours. They are commonly used for receiving organic excretions of sick persons in the same way as carbolic acid is used, and have about three times the power of carbolic acid to destroy bacteria.
They have one great advantage besides the strength mentioned, in that they are not materially affected or interfered with by the presence of albuminous material. Carbolic acid in the presence of albuminous material, like sputum, for instance, has the strength of the disinfectantpartly used up in combining with this albuminous material so that the strength remaining for disinfection is weakened, and the result is not as satisfactory as it would otherwise be. The coal-tar products, on the other hand, are not so interfered with, and the solution acts in full strength upon the bacteria.
Mercury for disinfectant.
Corrosive sublimate, or bichloride of mercury, is one of the most active poisons known and is as effective in dealing with the microscopic organisms known as bacteria as it is in dealing with the larger animals for which it has been used for years past,—the destruction of bed-bugs.
For general cleaning purposes, such as scrubbing woodwork, floors, and walls, it should be used in strength of about 1 part to 3000 parts of water. This means that for 1 ounce of corrosive sublimate 3000 ounces of water or 25 gallons must be taken. This solution is very active in its effect on all metal, so that it must be kept in brassware or earthenware, and when mixed with the material which it is intended to disinfect, it must be kept from tin or iron. This solution is also affected by albuminous material, although this may be counteracted by the addition of salt. It is a good plan, therefore, to add to the solution salt at the rate of about 4 teaspoonfuls to each gallon of solution. On account of the very poisonous action of this solution great care must be taken to keep it away from children, and it has been suggested that it is desirable to add some coloring matter to the liquid, since without this it may be mistaken for clear water.
Lime for disinfecting.
Chloride of lime is one of the most useful as well as oneof the cheapest disinfectants available. It costs about $25 a ton, although by the pound this wholesale price would not be obtained. It is effective in a 1 per cent solution, that is, 1 pound of chloride of lime to 100 pounds or 12 gallons of water. To be effective, the solution must be well stirred into the organic matter to be disinfected, since it is the chloride rather than the lime which is the disinfecting agent. Saucers or soup plates of chloride of lime standing around the room have no effect upon the germs in the air and on the floor and are of no more value than sulfur, or roses for that matter. Chloride of lime is commonly known as bleaching powder, and its effects on clothes or on any substance which can be eroded is well known. It is, therefore, not a suitable material for disinfecting towels, because the action is on the towel as well as on the bacteria, differing in this respect from mercury, which does not hurt the fiber of clothes.
Milk of lime is produced by slaking ordinary building lime until a fine white powder is obtained, about an equal quantity of water to the amount of lime to be slaked being necessary. When the powder has formed and steam has ceased to be given off, then about four gallons of water should be added to each gallon of the powder and the mixture well stirred. This will probably always leave some lime in the bottom of the vessel, since limewater is a saturated solution, and these proportions furnish more lime than is necessary. If not too thin, it is a good whitewash and is a most important agent when used as a whitewash in disinfecting walls and ceilings of such rooms as hospitals and cellars and other places where have been contagious diseases. Milk of lime is an admirable disinfectant in thesick room and generally in houses where infectious diseases have been. It may be poured down drains, into water-closets and privies, and used liberally in all places where bacteria may be supposed to thrive. It must come into intimate contact, however, with the bacteria, and merely sprinkling a little lime dry around the borders of a gutter or drain is of no value. The writer saw, not long ago, a chicken yard where the inspector of a health department had undertaken to secure disinfection by a generous sprinkling of white lime powder around the yard. Such a procedure, however, is not effective, but in a drain the dry powder might be of value because it would later become effective when washed in solution into the drain. Ordinarily, the dry powder is to be avoided.
Soap as an antiseptic.
No better antiseptic exists than ordinary soap, not altogether because of the properties of the soap, but because of the action of the soap combined with hot water. Washing soda, dissolved in water and used for boiling clothes which have become polluted, adds to the disinfecting power of the hot water the disinfecting properties of the soap, and the result is most effective. Ammonia has not the same value as the soda or potash soap, although it has the power of destroying bacteria in the course of a few hours.
It may not be out of place to emphasize the value of soap, not particularly in times of epidemic or contagious disease, but as a continual safeguard against infection. A large proportion of the contagious diseases are probably the result of infected fingers or hands coming in contact with the mouth and leaving there the germs of infection. Oneof the first things a surgeon learns, in order to avoid any possible infection of wounds or of openings which he makes for an operation, is to thoroughly wash his hands in order to remove therefrom all possible germs. He scrubs his hands, particularly his finger nails, with soap and water and then bathes them in a solution of bichloride of mercury before touching the patient in any place where infection might occur. The difficulty, even with this great care, of freeing their hands from bacteria has been found to be so great that, in late years, surgeons have preferred to use, during operations, thin rubber gloves which can be boiled before using and can be soaked in a stronger antiseptic than the hands could bear.
It is extraordinary, from the standpoint of self-infection, to see how men can be so careless as to sit down to dinner, after having worked in places where their hands have come in contact with all sorts of organic filth, without stopping to wash those hands even in cold water. It is certainly providential that disease germs are as uncommon as they are, for with the careless habits of most people in putting their hands to their mouths, the death-rate from infectious diseases would be much higher than it is except for the fact that most of the germs thus introduced into the mouth are not disease-producing.
Disinfecting by heat.
Better than any chemical agent known to be a destroyer of bacteria is heat in one form or another. This may be steam or hot water or dry heat. If a high enough temperature is maintained for a sufficient length of time, the action is absolutely destructive to all germs. Fire does, of course, destroy bacteria along with whatever material the bacteriaare concealed in, but such a disinfectant is of little value for ordinary purposes, since the object of disinfection is to destroy bacteria without destroying the surface on which they are lodged. In some old buildings, where consumption or smallpox, for example, has become permanent, it may be that the surest way of killing all the bacteria is to burn up the house.
Dry heat.
Unfortunately, even a moderate heat cannot always be applied. One's hands, for example, can neither be heated in an oven to the necessary temperature for destroying bacteria in their pores, nor can they be immersed in boiling water or steam for a sufficient time to secure thorough disinfection. Therefore, with the body, chemical means for disinfection must be employed. Also when it is desired to disinfect a liquid, such as beef broth, in which the experimenter desires to grow some particular species to the exclusion of all others, dry heat is inapplicable because it would evaporate the liquid, nor is chemical disinfection possible because of its antiseptic effect on the bacteria to be cultivated. Moist heat, therefore, must be used. When dry heat is used, it is usually for the disinfection of glassware or earthenware or metallic objects, the quality of which will not be affected by the necessary temperature, namely, 150 degrees Centigrade, or about 300 degrees Fahrenheit. This temperature must be maintained for at least an hour, and it is not certain even then to penetrate in full power to the middle of blankets or comfortables. Except for glassware to be used in a laboratory, dry heat, such as would be obtained by a kitchen oven, is not to be recommended.
Boiling water.
Boiling water, on the other hand, is the most effective and penetrating disinfecting agent available. One has only to expose an object to boiling water for five minutes to absolutely kill all disease-bearing bacteria contained, and since bed linen, clothes, blankets, and such articles as are naturally used in a sick room have to be washed after a patient's recovery, it requires but very little additional trouble to subject the soiled articles to that temperature of the water which will secure disinfection at the same time. But the water must be boiling. The mere fact that it was once boiling water gives it, half an hour later, no disinfecting properties, and complete disinfection can be secured only by actually boiling the garments or articles for at least five minutes. The apparatus necessary therefore—and no better piece of disinfecting apparatus can be secured anywhere—is a good old-fashioned wash boiler. The action is more certain, that is, more penetrating, if a little washing soda is added to the water at the rate of a tablespoonful of soda to a gallon of water. This solution is admirable for washing dishes, spoons, knives, forks, and other eating utensils used by sick persons. It is always a mistake to wash dishes from the sick room in the same vessel with other dishes. They should not only be washed separately, but they should be washed in boiling water, and preferably in a soap solution as just described.
Steam.
For some purposes, steam is better even than hot water; its effect on cotton and woolen garments is not so disastrous. A comfortable or blanket, for instance, may be subjected to steam without losing its elastic quality, andfor small garments, an ordinary steamer, such as is used for puddings, answers admirably. Cities use steam sterilizers because of the greater convenience in furnishing steam to a large tank as compared with filling and emptying a tank with water and then providing sufficient heat to boil that water. The exposure to steam should last from half an hour to an hour, depending on whether the objects to be disinfected are small, open, and loose, or large, compact, and dense. Some articles, like bales of rugs, rolls of wool, and large bundles of cloth, cannot be sterilized at the center by ordinary steam, and while it is not likely that infection at the centers of such tightly rolled bundles has occurred if exposure took place while rolled up, yet it is certain that the disinfection does not reach these centers. In the case of such bundles as rugs from infected countries, where any single rug may become the medium of infection, it is requisite to thoroughly sterilize all parts of the bundle. For this purpose, it is necessary not merely to expose the articles to live steam, but to have the live steam under pressure so that it is forced into the inside of the packages by an excess of external pressure. This is probably not available in an ordinary house, where boiling must continue to be the method of disinfection.
Drying, light, and soil.
Before leaving this chapter, three agencies for disinfection may be pointed out, not perhaps to be depended on, but in order that the kindly provisions of nature may be appreciated. All germs removed from the body, which is their natural home, and exposed to the air are subject to drying and thus are killed. Unfortunately, this does not become true except after long periods of time, nor is itequally true with all germs, but it is certainly one of the methods by which the evil effects of disease germs may be lessened. The germ of consumption lasts as long as any germ, and yet this, when dried in the street, loses its vitality after about a week. Similarly, the typhoid fever germs, unless kept in a moist condition, dry up and die in a few days. With the drying, however, comes the danger that in the process they may be lifted by the wind and carried in the air to the mouths or nostrils of well persons, so that it is not wise to depend solely on this method of disinfection.
Sunlight is more positive than the wind, and the exposure to direct sunlight of a bottle filled with disease germs will kill them all in two or three hours. The surface layers of a pond never have as many bacteria in them as the lower layers, partly on account of the sedimentation, but largely because they are killed by the direct action of sunlight. The bacillus of consumption and bacillus of diphtheria are both killed in an hour or so by direct sunlight. This is one reason why living rooms should have sunny exposure and why, on the other hand, disease thrives in dark tenements.
The soil is the third natural method of disinfection, not because the soil itself destroys bacteria, but because in the soil are to be found millions of non-harmful germs and these germs are hostile to the disease-producing germs, so that they destroy their virulence. It is on this principle that the wastes from typhoid fever patients are buried in the garden, the presumption being that the bacteria there present will destroy the typhoid fever germs before they can escape and do any harm. While this action undoubtedly exists, it is not positive enough to depend upon, and disinfection by the use of chemicals should always be practiced.