Under air-borne diseases, by a somewhat loose usage, we may include a long list of diseases in which the channels of entrance and exit are the air passages. The medium of transfer is the air, in which the bacteria, usually breathed, coughed, or sneezed out in droplets, pass from person to person. This group of infections includes some of the most important diseases which affect mankind. This group would still be of the utmost importance if it included no diseases in addition to tuberculosis and pneumonia, which have been running a close race to see which could kill the more people in a year. Just at present pneumonia is in the lead, but pneumonia cannot compare with tuberculosis as a cause of poverty and social ills. Smallpox, diphtheria, and the so-called children's diseases—measles, scarlet fever, whooping cough, and chickenpox—are all transferred by the droplet method. In some of these diseases we do not know the actual germ, but it has been shown that they are carried from person to person in the air.
In this group of diseases the disease itself may or may not be confined to the respiratory tract which merely serves as a channel of exit and entrance. The micro-organisms of such diseases are usually borne in minute particles of moisture. These droplets are given off through the nose and throat, and another person may or may not be infected by them. The spread of the infection depends upon three things: the number of organisms, the virulence of the organisms, and the resistance of the individual.
In some instances the vitality of the causative microorganism is so slight outside the human body that the infection must be passed immediately from person to person. This is frequently loosely called contact, since, to be infected, the victim must come within a short distance of the infected person. This is the case in whooping cough. In other instances the microorganisms are hardy and live for some time outside the body and close association may not be necessary. This seems to be particularly true of the tubercle bacillus. The sputum of a tuberculous individual may, under favorable conditions, contain the living bacilli for days and even weeks.
Coughs and Colds
Coughs and colds are transmitted in this same way, but in regard to the micro-organisms which cause colds there is a complicated bacteriological tangle. Certain epidemics of colds are apparently caused by the pneumococcus; others by the influenza bacillus, and still others by various organisms. The microorganism of the common cold has not been discovered, although the researches of Foster suggest that he has isolated the specific bacterium. Attempts have been made to use a vaccine against colds, but they have been of little success, for the reason that the immunity conferred by the disease is short and, further, because we do not yet possess sufficient knowledge of the bacteriology of colds. Colds are not always transmitted through the air. Careless people may infect others by contact, such as by using a common drinking cup or common towel, which may thus afford the infecting droplets an opportunity of entrance into the nose and throat.
Colds and the allied conditions tend to be self-limited. The infection is aggravated and prolonged by abnormal conditions of the nose and throat and by poor physical conditions, and so the remedial measures are directed largely against these two contributing factors. The cure of a cold is primarily brought about by the body itself, for there is no specific cure.
Colds are extremely infectious as is illustrated by the fact that a cold frequently "runs through" an entire family. We have already mentioned the tremendous economic loss and some of the sequelae of colds. Colds, like all the air-borne diseases, are difficult of prevention in contrast to the relatively easy prevention of the diseases caused by ingestion. This difficulty is well illustrated by the seasonal occurrences of colds. They are largely winter diseases, merely because in winter we have favorable conditions of spread. These conditions are the close proximity of persons, the closed rooms with the inevitable concentration of the infective droplets, and the usual lessened physical efficiency of winter.
The real danger in this so-called droplet method of infection is the actual proximity of the infected person. The prevention of colds and also of the other air-borne diseases is almost entirely an individual problem. It is incumbent on the individual to avoid and correct abnormality and irritation of the upper air passages and to keep his physical condition as nearly perfect as possible. Then, an intelligent appreciation of the method of spread of the air-borne diseases will enable him to Avoid wherever possible the close proximity of infected persons and to prevent the concentration of infective droplets in a closed place. Promiscuous coughing, sneezing, and spitting into any but proper receptacles are obviously dangerous and should be prohibited. The use of common utensils is also dangerous. At best, infection is always easy, but the individual can do much by developing proper habits to prevent these diseases. Since every case of infection is a starting point for other cases, the continuous prevention of a few cases will mean, in the end, a marked reduction or eradication of these diseases.
Influenza
True influenza is a distinct disease and is not an ordinary cold or "grippe." The disease is due to a specific bacillus which can be isolated readily and which, of course, is entirely distinct from the microorganism which causes the cold or "grippe." Influenza makes its appearance periodically and sweeps over the entire world in great pandemics. It usually starts in Russia and works westward through the continent and thence to the United States. The last great epidemic was in 1894. Since that time influenza has been with us constantly. The transfer and prevention are essentially the same as for colds and the latter depends on the general practice of good personal habits.
Diphtheria
The infection of diphtheria is caused by a bacillus, which is known, after its discoverers, as the Klebs-Loeffler bacillus. Diphtheria is also known as membranous croup. As a matter of fact some cases of sore throat are, in reality, unrecognized cases of diphtheria.
The disease has been recognized for many centuries, but it was not until 1821 that the clinical observations of Brentonneau, of Tours, established its separate identity. Diphtheria occurs in nearly all parts of the world, but it is most prevalent in the Temperate zone. While it occurs in epidemics and in sporadic cases and is endemic in nearly every large city, it is more common in the country districts. Diphtheria occurs most frequently between the ages of two and eight. One attack does not protect and may be followed by several attacks. It is not uncommon for people who take care of diphtheria patients to come down with the disease, but a goodly proportion of people are naturally immune and do not contract it under any conditions of exposure.
The incubation period of diphtheria, that is the time required for the development of the disease after the infection is received, is short, only one to five days. While the infection is largely conveyed by the air, a number of epidemics have been traced to infected food and drink, notably milk. The writer has recently traced an epidemic to infected salad dressing. Under favorable conditions diphtheria bacilli remain alive outside the body for weeks. As in a number of other diseases, there are carriers of diphtheria. Apparently healthy persons without sore throats and others after recovery from diphtheria harbor the micro-organisms in their throats for varying lengths of time. These people often spread the disease.
The diagnosis of diphtheria can usually be made by an examination of the throat and the symptoms. The only positive method, however, is the examination after twenty-four hours of the organisms which have grown on suitable media from the secretions of the nose and throat.
The average mortality from diphtheria has been reduced one-fourth or more since the introduction of antitoxin in 1894. The duration of the individual attack has been shortened and its severity lessened.
Moreover, through the use of prophylactic injections of antitoxin, the spread of the disease has been checked and numerous epidemics brought to an end. In one hospital, February to June, 1894, 448 children were admitted suffering from this disease and 109, or 24.5 per cent, died. Serum was used. In another hospital over a corresponding period of time, out of 520 cases 316 or sixty per cent died. Here no serum was used. With the improvement in antitoxin, an analysis of 80,000 cases that received it at any time showed a mortality of fifteen per cent. If antitoxin is used in the first two days of the disease, the mortality is under eight per cent.
In 1883, the year before the discovery of the diphtheria bacillus, which enabled a positive diagnosis to be made, 97 out of every 100,000 of the population of the eighteen largest cities of Europe and America died of diphtheria. Undoubtedly there were many more deaths due to diphtheria but attributed to other causes since an exact diagnosis could not be made. In twenty years the mortality had been reduced somewhat, due largely to the ability to make an early diagnosis and to quarantine. In 1900 in the United States registration area the mortality from diphtheria was 43 per 100,000. The decline since 1900 is relatively greater than that shown by any other important cause of death. The decline in the mortality is much greater in diphtheria than in any other of the air-borne infections and must be attributed to the increasing use of antitoxin. It must be remembered, furthermore, that even today a large proportion of the fatal cases of diphtheria either do not receive antitoxin or only when moribund. The antitoxin reduces the mortality from diphtheria in two ways. Given to the patient it acts as a cure for the disease. Given to exposed persons it protects them from contracting the disease. To be sure the protection afforded is short—only two to six weeks—but that is sufficient to protect during the course of an ordinary epidemic.
Diphtheria antitoxin is a substance, or substances, in blood serum, usually of a horse, which neutralizes the poison or toxin given off by the bacillus of the disease. In the case of the diphtheria bacillus, the toxin is a poison which is not in the bacteria itself, but which is diffused throughout the system of the individual. Recovery depends on the presence of antitoxin which may be produced naturally by the body or supplied artificially. The blood from a horse, which has had diphtheria toxins injected repeatedly at suitable intervals, neutralizes the poisons of diphtheria in enormous amounts, but not at all the poisons or toxins of other bacteria. The fluid part of the blood of such a horse, after coagulation, which is known as serum, when given to the patient suffering from diphtheria, will neutralize all the poison of diphtheria in the body of the patient. The effect is due to the antitoxin in the serum and not to the serum itself, although serum and antitoxin are sometimes incorrectly assumed to be synonymous. Diphtheria antitoxin was the first and it is still the most effective antitoxin we have. The effects of the diphtheria antitoxin disappear rather rapidly and only protect for a short time. In other words, the antitoxin will not protect for any longer time than an attack of the disease.
It should be rather easy to stamp out diphtheria, because there is available an early method of diagnosis by means of cultures taken from the nose and throat, the cure of the disease itself by antitoxin, and the prevention of transmission of the disease by making all exposed persons immune through the use of antitoxin. Furthermore, it is possible to tell by bacteriological examination at what time the patient ceases to harbor the micro-organisms and by the same simple method detect carriers. This examination is so important that it is performed free of charge by all state boards of health and by the boards of health of most cities.
There has been perfected recently a test which shows whether a person is certainly immune to diphtheria (Schick's test for antitoxic immunity). This test enables us to determine a percentage of those persons who are actually immune. While the reduction in the diphtheria mortality has been marked, yet it is the failure to utilize these additional weapons which we have in diphtheria as in no other disease, which explains why this disease has not been practically eradicated. Unlike most air-borne infections, early diagnosis by the bacteriological examination is easy and accurate and thus prevention by quarantine and isolation not only of those actually sick but of all carriers is unusually effective. In handling a case of the disease great care should be used in the disposal of material contaminated by the secretions, for, under favorable conditions, the diphtheria bacillus may be long lived outside of the body. Fortunately, the bacillus is easily killed by the ordinary methods of disinfection.
The claim is sometimes made that antitoxin works harm. It is argued that lockjaw and various loathsome diseases are introduced into the body with the antitoxin. Since the horse is not susceptible to and cannot carry most human diseases, including syphilis, the introduction of disease must be due to gross carelessness in the handling of the serum. Obviously every precaution should be taken in securing the serum. All sera are now licensed by the U.S. Public Health Service, and in Massachusetts and other states, the state itself produces the antitoxin and guarantees its purity.
Some eight to ten days after the injection of antitoxin certain patients have rashes and, rarely, joint pains. This condition, called serum sickness, is transitory and is due to the injection of a foreign serum. Thus it is a mild manifestation of anaphylaxis. In very rare cases (less than a hundred have been collected) severe anaphylaxis and death may develop immediately after the injection of the serum. In most cases the individual had previously shown marked susceptibility to horse protein, usually in the form of asthma when near horses. Individuals with a history of horse asthma should receive antitoxin produced in some other animal than the horse.
Children's Diseases
The term "children's diseases" means that such diseases are so contagious that an individual will catch them as soon as he goes out and mingles with his fellow beings. All of the children's diseases are spread by the droplet method of infection. We include in this category, as a rule, measles, scarlet fever, chicken pox, mumps, and whooping cough.
Measles. Measles has been known for so long and through so many generations that the race has acquired a certain immunity to the disease. A moderate protection is conferred by one attack of measles, and second attacks are not common. The incubation period of measles (the time from exposure to the development of the disease) is nine to eleven days.
The exact cause of measles is unknown, but we do know that it is a disease peculiar to man, although it can be given to animals. In common with a number of other diseases, measles starts as an ordinary cold, but the rash, which is the only way in which we can diagnose the disease, may not appear until the person has been ill for three or four days. Experimentation has shown that the poison has been in the blood and nasal secretions before that time. This is an important point, because it means that people, usually children, wander about thinking that they have an ordinary cold. Then they come down with measles after spreading the disease far and wide. The prevention of measles is difficult for this reason. So far as we know, measles is spread almost entirely by the droplet method from secretions of the nose and throat, just as are colds, but measles are, if anything, the more "catching".
There is no evidence that measles is spread from the skin, and the scaling of measles, often regarded as highly dangerous, probably never carries the disease. Possibly there are carriers of measles or the disease may be transferred by a third person. However, this point is not established by bacteriological examination, since we do not know the organism. All our evidence points to the immediate transfer from person to person, particularly in the preeruptive stage before the diagnosis is possible and also by unrecognized cases.
Measles is notoriously communicable, but close proximity to patients or discharges from the nose and throat seems to be the determining factor of infection. For example, measles can be cared for in the same building or in the same ward with other patients and the disease will not spread. But this requires the most scrupulous precautions of asepsis. The disease is not air-borne in the sense that a current of air from the room of the patient with measles carries the infection into another room. The method of infection seems to be the transfer of the moist secretions of nose and throat by the droplets of coughing or sneezing in the air or by contaminated hands and the like. Disinfectants and fumigation after the convalescence of the patient are of little importance. The strictest precautions should be observed in the possible transfer during the course of the disease. In epidemics rigid quarantine is necessary not only for those with the disease, but also for those exposed until the incubation period of ten days is past.
Measles is usually regarded as an innocuous disease, but measles and its sequelae, especially pneumonia, cause many deaths. As a rule it leads scarlet fever in the mortality tables, but in 1914 measles was exceeded by whooping cough. German measles is merely a mild disease very similar to measles.
Scarlet Fever. Scarlet fever is one of the most important of the children's diseases from every standpoint. We do not know the exact cause of the disease, although Dr. Mallory, of Boston, has made a preliminary report on a bacillus which may be the infecting agent. Scarlet fever is usually transmitted through the air by the droplet method, but there have been several large epidemics in which the disease was carried by milk. Scarlet fever is not so communicable as measles. It may be carried from one person to another by an indirect method either by persons or by inanimate objects.
Scarlet fever is contracted through the nose and throat. The onset of the disease is usually from two to five days after exposure, and the first symptom is usually a sore throat which antedates the eruption by one or two days. Incurable nephritis (kidney disease) is frequently traced to an earlier attack of scarlet fever. Valvular disease of the heart is another sequelae. In some epidemics of scarlet fever the immediate mortality reaches thirty per cent, but this is unusual. The danger in scarlet fever is on account of the remote complications. Measles is the immediate cause of more deaths than scarlet fever, due not to the measles itself, in which the mortality is low, but to the immediate complications, especially of the lungs. Yet scarlet fever is a more serious disease than measles on account of the frequency and severity of the remote complications like nephritis and heart disease.
One attack of scarlet fever seems to protect against another attack, but cases of individuals having it twice are by no means rare. Since we do not know the organism of the disease, the recognition of the length of infectivity of a patient, of carriers, and of mild cases is impossible. Like measles, the disease is usually only to be diagnosticated by a rash which is by no means the initial symptom. Prevention is extremely difficult. All the evidence points to the transmission from the discharges of the nose and throat and the disease probably gains entrance in the same way. For years the period of scaling, which occurs late in the disease, was regarded as the main infective period and the scales were considered to carry the disease. There are unquestionably scarlet fever patients who spread the disease after recovery, but, almost invariably in these cases, the early inflammatory condition of the nose and throat has not entirely subsided. For the release of patients from quarantine a normal nose and throat seem to be a fairer criterion, both to the patient and the public, than the absence of scaling.
The writer is familiar with a case of scarlet fever in which, before the eruption appeared, a surgeon performed tracheotomy to prevent suffocation. The next day the child showed a typical rash of scarlet fever, and later the surgeon developed the disease. As the surgeon operated with gloves and in a surgical gown, the presumption is that the infection was by droplets from the throat before the eruption occurred. Scaling was much delayed in the case of the surgeon and it was afterwards learned that he mingled with people to such an extent that if the scales carried the disease widespread infection should have occurred. In point of fact no case developed. Such incidents could be multiplied.
During the course of scarlet fever not only should active and strict quarantine be employed for actual cases but also isolation in an epidemic for all sore throats and exposed persons. As in the case of measles, quarantine need not demand separate buildings as the air itself is not dangerous as it passes over and from the patient. The danger lies in particles of infective material from the nasal secretions, usually carried in small droplets directly to the nose and throat of other people, but these particles can be transferred in many ways during close proximity. The proximity of handling, for example, is dangerous. So all secretions of the nose and throat should be disposed of carefully. So-called terminal disinfection after the disease may be used, but it is of doubtful value.
Chicken Pox. Chicken pox is a mild disease which results from some unknown cause. One attack seems to protect against another attack. The incubation period is probably about twelve days. From the point of view of health chicken pox is not a dangerous disease. The onset is usually as a cold, so the methods of transmission and prevention are presumably the same as those for colds, measles, and scarlet fever. Mild unrecognized cases frequently spread the disease.
Mumps. Mumps is another of the so-called children's diseases. Mumps is characterized by a swelling of the parotid and sometimes of all of the salivary glands. Here again we do not know the cause of the disease, but it is presumed that the infecting agent is a micro-organism. The incubation period is about three weeks. One attack gives only moderate protection against a subsequent attack. With the exception of the fact that mumps causes no rash, it is similar to measles, scarlet fever, and chicken pox. The methods of transmission and prevention are the same. Here, again, the person may not know that he has the disease and so spread the infection. Any fatality from mumps is an excessively rare occurrence. A not uncommon complication of mumps is the involvement of the testicles in the male and the ovary in the female. If both testicles of the male are involved, sterility may result.
Whooping Cough. Whooping cough belongs in the group of children's diseases. We know that the causative agent is a small bacillus which has been isolated. Whooping cough is an important cause of disease and death among children, and in weak, puny children it is apt to cause serious complications. While the disease in itself may not be especially serious, deaths due to it directly or indirectly are rather common. In 1914 whooping cough was given as the cause of more deaths than measles or scarlet fever. The mortality figures vary widely from year to year and there seems to be no general tendency to increase or decrease. One attack of whooping cough more or less prevents other attacks. Attempts have been made to secure a vaccine or antitoxin, but the difficulty lies in the early recognition of the disease, for it may go on for a week or so before it is recognized. Even after recognition the disease, and sometimes the infectivity, may persist for weeks.
Whooping cough is usually only communicable by immediate association. The infection is presumably carried from the secretions of the nose and throat, but it seems to be short lived outside the body and only transferable for short distances. Some of the domestic animals seem to suffer from whooping cough and may transfer the disease. The prevention is by quarantine of the victim. Fumigation is unnecessary, but the proper disposal of the discharges from the nose and throat is important.
General Considerations in Diphtheria and the Children's Diseases. All these diseases have certain characteristics in common. All apparently originate in the nose and throat, and most of them start like a cold or sore throat and may be difficult of recognition in the early stages. Ever since we have had statistics of disease, we have had little diminution in the children's diseases, with the exception of diphtheria. And until we know the precise causes of the infections we cannot know the precise methods to combat the diseases. We have frankly to admit that in combating this group of diseases we have not been very successful. Isolation has not been successful. But we can point out that smallpox, the worst of these airborne diseases, has been prevented by vaccination.
With the exception of diphtheria, the chief dependence for the prevention of the spread of this group of diseases is by quarantine. And yet, due to the difficulties of diagnosis, the cases are often at large when perhaps most dangerous. The general method of boards of health in combating these diseases is to placard the house of the victim, which makes a sort of quarantine or isolation. In measles the attendants are allowed to go about. More precautions are taken with scarlet fever. These methods are, of course, important, particularly where they include the isolation of suspects and exposed persons, but they are probably of greatest moment in the education of the people to a knowledge that these diseases are communicable.
The efficiency of quarantine can be tested by the examination of statistics. While quarantine has doubtless prevented widespread epidemics, yet, in the main, scarlet fever, whooping cough, measles, mumps, and chicken pox go on in much the same amount now as formerly. But not so with diphtheria. During the same period—since 1880—the prevalence of diphtheria has been reduced enormously, but in this case we have the use of other means than quarantine. In addition we may recall the ineffective control of smallpox in Germany by the most rigid quarantine. Quarantine should not be given up, but it seems certain that such diseases as are spread from the secretions of the nose and throat and are presumably carried in the form of droplets, either in the air or in discharges, more or less directly to other people, can be eliminated by quarantine very slowly if at all.
Then, too, we are inclined to speak of quarantine as a fixed thing. Chapin, of Providence, has done much to upset our complacency about quarantine. What is effective quarantine for one disease on account of definite characteristics of the disease and the micro-organism, may not be at all effective for another. In the past we have taken elaborate precautions about the transfer of air, but our efforts were probably wasted. Smaller and larger particles of the secretions of the nose and throat are the dangerous agents. These particles as "droplets" are propelled directly by coughing into the noses and throats of other people. In addition, these particles, especially with children, can be transferred on common utensils, common toys, and the like. Nasal discharges and sputa carry the infection and preserve the life of the infecting bacteria. But these infections are probably not air-borne in the sense that ordinary air conveys the infection to direct points. They are air-borne only as the droplets stay in the air. The term "contact", meaning proximity, is being applied more and more to this type of case. The quarantine, as Chapin has shown, should be directed towards the possible transfer of the nasal or buccal secretions. This includes droplets in the air, all utensils, and the like. Further, it puts precautions on the attendants. Under such conditions patients will not infect others in the same room. But, on account of human frailty, it is desirable to leave a wider gap than this between infected patients and others, and thus the desirability of continuing quarantine. Until we have additional methods of prevention, like vaccination against smallpox, the early diagnosis, and the curative and prophylactic antitoxic serum in diphtheria, we must not expect too much of quarantine.
In addition to quarantine, much or more can be accomplished in the way of prevention by sound habits of hygiene on the part of the individual. Everyone should be extremely careful of all infections of the nose and throat. Any cold is a possible beginning of any one of these special infections, and this is another point in favor of a reasonable quarantine of the ordinary cold. In general, the prevention of colds and the prevention of these air-borne and contagious diseases depends upon the same factor,—that of personal hygiene. Quarantine will always be necessary as a public measure, but personal hygiene is of greater importance and should be so regarded.
Fumigation may or may not be of value. It often gives a false sense of security, for the so-called terminal fumigation is usually carried out when, by the nature of things, all the infecting micro-organisms have died out. Fumigation may be perfectly scientific, but, when we do not know the cause of a disease, our fumigation is entirely experimental since there are no means of checking it up. Again the value lies in the education of the people by giving them a concrete example of the fact that the disease is communicable. The simplest and probably the most effective method of fumigation is to open the windows and let in the sunlight and fresh air and not allow the room to be occupied for a few days. Thorough mechanical cleaning with soap and water is probably of value.
Pneumonia
Next to tuberculosis in importance is pneumonia. This disease causes ten per cent of the deaths in the United States each year. Formerly tuberculosis caused more deaths than any other disease, but now pneumonia ranks with the "Great White Plague." The death rate from pneumonia fluctuates widely from year to year and one is inclined to suspect the accuracy of some of the records of deaths. In 1900, the death rate from pneumonia was 180.5 per 100,000, and in 1914, 127 per 100,000. The figures for 1914 were the lowest on record, but with the general reduction of deaths pneumonia now causes a greater proportion of the mortality than formerly.
Pneumonia may be defined as an inflammation of the lungs and the usual cause of the disease is a bacterium belonging to the coccus group, the pneumococcus. The disease attacks people of all ages, in all climates, of both sexes, at all times of the year. Old people are particularly apt to be carried off by it, as are people in poor condition, especially the chronic alcoholics. Pneumonia occurs in early life and is moderately fatal, but in old age it is so fatal that it is called "the friend of the aged." In middle life the mortality varies. Roughly the mortality from pneumonia runs about twenty per cent.
Pneumonia is another of the self-limited diseases. Recovery from pneumonia is extremely rapid. When the disease has run a typical course, the fever often drops suddenly to normal, a so-called crisis. The immunity afforded by an attack of the disease lasts only a short time, and people who have had it once are rather more liable to have it again. It is evident, therefore, that if the disease does not protect against another attack, certainly no vaccine will.
Pneumonia was formerly considered one of those diseases which "happen", and there was considerable difficulty in recognizing that it was communicable. The discovery of the pneumococcus as the cause of the disease did not solve the problem. Pneumococci are found in many normal mouths and the same organisms are, furthermore, the cause of colds, tonsillitis, and other more or less mild disturbances. While there are on record a number of definite epidemics of pneumonia, it is rare for doctors and nurses to contract the disease in their care of patients. Then, in all general hospitals patients suffering with pneumonia are, as a rule, cared for in the open wards and cases among the other sick do not develop. It has been suggested that, since the pneumococcus is a rather easily destroyed organism, ordinary proximity is not dangerous. Another suggestion is that the factor of resistance may be the determining factor. Yet these suggestions do not explain adequately the enormous number of cases of pneumonia. As a matter of fact we have no complete solution, but recent researches, especially at the Rockefeller Hospital in New York, have given us much additional knowledge.
We now know that pneumococci may look alike and grow in the same way, but still be different. There are at least four groups of pneumococci. The pneumococcus present in the normal mouth is not found in the form of pneumonia with a high mortality. Still, not only the patient, but those who care for the patient, may harbor in their mouths for a few weeks not the ordinary mouth pneumococci, but the pneumococci of that particular pneumonia. These facts were brought out in the attempts to secure an antitoxic serum for pneumonia. It was found that the serum of a horse, highly immunized by a particular pneumococcus, contained abundant antitoxin, but that this antitoxin was only effective against the toxin of that one type of pneumococcus. The story of these attempts to find a serum and to identify the various types of pneumococci is complicated and is only just begun. It is sufficient to say that, in spite of tremendous obstacles, sera have been developed, which are promising of future achievements, but as yet no such brilliant results as are seen in diphtheria antitoxin have been attained.
In the meantime, while the mechanism of infection in pneumonia is not entirely clear, pneumonia should be seriously regarded as a communicable disease. Considerable quarantine should be enforced and strict precautions should be taken to disinfect all the excretions of the patient, particularly the sputum. We still lack the necessary knowledge to expect successfully to combat the disease or to prevent it to any marked degree.
Tuberculosis
Tuberculosis is an infectious disease which is caused by the tubercle bacillus. The disease may infect any tissue of the body and may assume a wide variety of manifestations, but the most common form of tuberculosis is that of the lungs—consumption or phthisis. Five-sixths of all the cases of tuberculosis and of the resulting mortality are due to consumption. But it must be remembered that it is the same bacillus which causes all forms of tuberculosis and that the non-pulmonary forms of the disease may be fatal and a focus of infection.
Tuberculosis of the lungs or consumption was well known to the ancient physicians. Babylonian tablets contain accounts of the disease, and Hippocrates (B.C. 460-376) gave a lucid description of it. The latter taught that "the consumption came from the consumptive", that "if the patient is treated from the beginning, he gets well", that change of residence is beneficial, and that "the most dangerous disease and the one which proves fatal to the greatest number is consumption." But the teachings of Hippocrates were disregarded until the middle of the nineteenth century. In general, consumption was regarded as a manifestation of Divine displeasure. It was usually considered to be hereditary and the best medical authorities taught that the disease was not catching. Consumption seemed to be incurable. The sporadic attempts of a few medical men to furnish their consumptive patients with fresh air were ridiculed and the patient was confined to a heated, closed room in which remarkable precautions were taken to keep out sunlight and fresh air.
Knowledge concerning tuberculosis accumulated slowly. Bayle (1803) and Laënnec (1819) recognized the unity of all the various manifestations of tuberculosis. In 1865, through experimentation, the disease was transferred to animals. In 1882 appeared the epoch-making work of Koch announcing the discovery of the tubercle bacillus and describing its habits. Since that time we have been able intelligently to study tuberculosis in view of our knowledge of the cause. But increased knowledge has also brought an appreciation of the difficulties connected with the problem of tuberculosis.
Frequency of Tuberculosis. Autopsy examinations have shown that from forty to ninety-five per cent of persons dying from any cause have in their bodies some focus, usually healed, of tuberculosis. Furthermore, the incidence of tuberculosis at autopsy is nearly as frequent at fifteen years as in adult life. In this connection it is necessary to draw the important distinction between infection with tuberculosis and the disease of tuberculosis. The scar indicates that the person has, at some time, been infected with the tubercle bacillus, but the existence of the scar does not mean that the person was ever sick with the disease or that he was a source of infection to others.
But these facts and those of the known incidence of the disease permit the following deductions: (1) Most individuals have been infected with tuberculosis. (2) This infection usually occurs in childhood. (3) The infection is not usually followed by manifest tuberculous disease. (4) Manifest tuberculosis or tuberculous disease may develop many years after the infection. Thus we can explain the incidence of a case of tuberculosis apparently remote from a focus of infection. Of still greater importance is the application of all known measures to prevent not only infection, but the change from infection to disease.