Chapter 16

CAUSES AND PREVENTION OF SICKNESS

Diseases of two kinds have long been recognized: first, those transmitted directly or indirectly from person to person, like smallpox, measles, and typhoid fever; and second, diseases like heart disease and apoplexy, which are not so transmitted. These two classes are popularly called "catching" and "not catching;" the former are the infectious or communicable diseases, and the latter the non-infectious or non-communicable. The term contagious, formerly applied to diseases supposed to be spread only by direct contact, is no longer an accurate or useful term.

THE COMMUNICABLE DISEASES

The invention of the microscope, as we have seen, revealed the existence of innumerable little plants and animals, so small that even many millions crowded together are invisible to the naked eye. These tiny living creatures are called micro-organisms or germs. The plant forms are called bacteria (singular, bacterium), and the animal forms protozoa (singular, protozoön). The common belief that all or even most bacteria are harmful is quite unfounded. As a matter of fact, while not less than 1500 different kinds of micro-organisms or germs are known, only about 75 varieties are known to produce disease.

Most bacteria belong to the class of micro-organisms called saprophytes, which find their food in dead organic matter, both animal and vegetable, and cannot flourish in living tissues. These saprophytes act upon the tissues of dead animals and vegetables, and resolve them into simpler substances, which are then ready to serve as nourishment for plants higher in the vegetable kingdom. Thus the processes which we know as fermentation and putrefaction are due to the action of saprophytes. Higher plants in turn furnish food for men and animals, and so the food supply is used over and over in different forms, making what is known as the _food cycle_. If it were not for bacterial activities vegetation would be robbed of its supply of nourishment, and plant life would speedily end; destruction of plant life would deprive the animal kingdom of food and thus all life would become extinct. The saprophytes are consequently essential to the existence of both animals and vegetables.

There are, however, other organisms called _parasites_, which can exist in living tissues of animals or vegetables. The organisms at whose expense the parasites live are called their _hosts_. Parasites not only contribute nothing to their hosts, but generally harm them by producing poisonous substances or depriving them of food. Some parasites are able to lead a saprophytic existence also, but as a rule they live at the expense of animal or plant life. Pathogenic, or disease-producing, germs belong to the group of parasites. The pathogenic germs which find favorable soil in the body produce poisons called toxins. These poisons or toxins interfere with the bodily functions, and thus cause what we know as communicable disease. Communicable diseases are caused by specific germs only: that is, a certain disease cannot develop unless its particular germs are present; the germs of typhoid for instance, can cause typhoid fever only, and not tuberculosis or other disease.

A number of diseases are caused by micro-organisms that are now well known. Chief among these diseases are colds, septicæmia (blood poisoning), influenza, pneumonia, diphtheria, typhoid fever, tuberculosis, whooping cough, Asiatic cholera, bubonic plague, meningitis, tetanus ("lock jaw"), leprosy, gonorrhœa, syphilis, relapsing fever, typhus fever, glanders, and anthrax. Micro-organisms not yet identified probably cause the communicable diseases whose origin is not known with certainty. These include infantile paralysis, smallpox, scarlet fever, measles, mumps, chicken-pox, Rocky Mountain spotted fever, yellow fever, hydrophobia (rabies), foot-and-mouth disease. We can hardly doubt that the intensive laboratory research now in progress will reveal in the near future the specific germs of these diseases also.

STRUCTURE AND DEVELOPMENT OF PARASITES

The group of parasites consists of two general classes, the vegetable, and the animal. In the former class belong the bacteria, and in the latter the protozoa. The two classes are not sharply differentiated, but in general the vegetable parasites are less highly organized than the animal.

BACTERIA

SHAPE.--Bacteria are composed of single cells and are consequently called unicellular organisms. Under the microscope individual cells are seen to differ in size, shape, and structure. In shape bacteria show three different types; the rod-shaped (bacillus), the spherical (coccus), and the spiral (spirillum). The organisms causing typhoid fever for example are a variety of bacilli, those causing pneumonia are cocci, while those causing Asiatic cholera are spirilla.

SIZE.--Bacteria vary greatly in size. Average rod-shaped bacteria are about 1/25000 of an inch long, but there are undoubtedly organisms so small that they cannot be seen, even by means of the strongest microscopes we now possess.

MOTION.--The power of motion in certain species of bacteria is due to hair-like appendages called flagella. These flagella by a lashing movement somewhat resembling the action of oars enable the organisms to move through fluids.

MULTIPLICATION.--After bacteria have fully developed, each cell divides into two equal parts; the process of division is called fission. Each of these two parts rapidly grows into a full-sized organism. Then fission again takes place, so that four bacteria replace the original one. In each of the four, fission occurs again, and so the process of multiplication continues. As bacteria develop they group themselves in characteristic ways. Some, like the streptococci, arrange themselves in chains; the diplococci, in pairs; the tetrads, in groups of four; others in packets called sarcinæ, and still others, the staphylococci, form masses supposed to resemble bunches of grapes.

Under favorable conditions fission occurs rapidly; in some types a new generation may appear as often as every 15 minutes. Enormous multiplication would result if nothing occurred to check the process. But in nature such increase never continues unhindered, and bacteria, acting upon their food substances, produce acids and other materials injurious to themselves. Furthermore, lack of proper food, moisture, or favorable temperature, and competition with other organisms tend to prevent their unrestricted growth and multiplication.

SPORES.--Most bacteria die if conditions become unfavorable to their growth, but some enter into a resting stage. This stage is characterized by the development of round or oval glistening bodies called spores, which are of dense structure and possess an extraordinary power to withstand heat, chemicals, and unfavorable surroundings. Except in rare instances a single cell produces but one spore. As soon as favorable conditions of temperature, moisture, and food supply are restored, the spore develops into the active form of the germ; it may, however, remain dormant for months or years. Spore formation, however, occurs in only a very few varieties of pathogenic bacteria.

DISTRIBUTION.--Bacteria are very widely distributed in nature; they are in fact found practically everywhere on the surface of the earth. They are present in plants and water and food; on fabrics and furniture, walls and floors; and they are found in great numbers on the skin, hair, many mucous surfaces, and other tissues of the body.

PROTOZOA

The protozoa are the lowest group of the animal kingdom. Like bacteria they are composed of single cells so small as to be visible only under the microscope. They play an important part in causing certain diseases of man, especially in the tropics. Among the well-known human diseases of protozoan origin are malaria, amoebic dysentery, and sleeping-sickness. Protozoa also cause several wide-spread and serious plagues of domestic animals.

VISIBLE PARASITES

A few diseases are caused by parasites large enough to be seen with the naked eye. One of the most important is hookworm disease. This disease is caused by a tiny worm which penetrates the victim's skin and ultimately finds its way into the intestine. Other diseases also are caused by parasitic worms, such as tapeworms, pinworms, and trichinæ. The latter are acquired as a result of eating infected meat, particularly infected pork that has not been thoroughly cooked.

TRANSMISSION OF PATHOGENIC ORGANISMS

Pathogenic or disease producing organisms need for their development food, moisture, darkness, and warmth, conditions that exist within the human body. When one or more of these factors is unfavorable, development of germs is checked; if unfavorable conditions are extreme or long continued, the organisms begin to die. It is difficult to say at exactly what moment they will die if deprived of moisture or exposed to extremes of temperature or other unfavorable conditions, just as it would be impossible to state at exactly what moment a collection of house plants would all be dead if water were withheld, or if the room temperature were greatly reduced.

Most pathogenic organisms, however, do not flourish long outside the body, and owe their continued existence to a fairly direct transfer from person to person. They gain access to the body through mucous surfaces such as the respiratory and digestive tracts, and through breaks in the skin, such as cuts, abrasions, and the bites of certain insects. They leave the body chiefly in the nasal and mouth discharges, as in coughing, sneezing, and spitting, in the urine and bowel discharges, and in pus or "matter."

The problem of controlling communicable diseases, consequently, lies in preventing the bodily discharges of one person from travelling directly into the body of another. If a person is not expelling pathogenic germs, it is clear that he cannot pass diseases on to others. But both pathogenic and harmless germs follow the same routes from person to person, so that safety as well as decency lies in preventing so far as possible all exchanges of bodily discharges.

There are five routes by which the bodily discharges most frequently travel from one person to another. Four of these routes of infection are called public, because in most cases efforts of individuals alone are not sufficient to control them. The public routes are water, milk, food, and insects. The fifth, or private route, includes all means by which fresh discharges of one person are passed to another, as when nose and mouth discharges are carried in coughing, sneezing, and kissing, or when bowel and bladder discharges are carried by the hands. These five routes in a given case differ greatly in relative importance, but the fifth, or direct route plays an immense part, although its importance in causing sickness has only lately been recognized. It cannot be too strongly emphasized that the chief agent in the spread of human diseases is man himself, and the human hand is the great carrier of disease germs both to and from the body. If unclean hands could be kept away from the orifices of the body, particularly the mouth, many diseases would soon cease to exist.

Defenses of the Body

In view of all the dangers from disease-producing germs it may seem surprising that the human race has not long ago succumbed to its invisible enemies. But the body has various defenses by means of which it may prevent invasion, or successfully combat its enemies in case they do gain access.

The unbroken skin is usually impassable to bacteria. Virulent organisms are often found upon the skin of perfectly healthy persons, where they appear to be harmless unless an abrasion occurs which affords entrance into the deeper tissues. Most bacteria breathed in with the air cling to the moist surfaces of the air-passages and never reach the lungs.

Mucous membranes lining the mouth and other cavities of the body would prove favorable sites for the growth of bacteria if the mucus secreted by them were not frequently removed. The mouth of a healthy person may contain bacteria of many kinds, but the saliva has a slight disinfectant power and serves as a constant wash to the membranes. The normal gastric (stomach) juice is decidedly unfavorable to the growth of bacteria, although it does not always kill them; they often pass through the stomach and are found in large numbers in the intestines. Other bodily secretions, such as the tears and perspiration, tend to discourage bacterial growth.

Tissues of the body vary greatly in their power to resist invading germs, so that the route by which germs enter influences the severity of their effects. Typhoid bacilli and the spirilla of Asiatic cholera when taken with food or water produce far more serious disturbances than when injected under the skin; infections from pus germs through an abrasion of the skin may result in a slight local disturbance, while the same amount introduced into a deeper wound might cause a fatal infection. Certain germs nourish in certain tissues only; even tuberculosis, which attacks practically all tissues, has its favorite locations.

IMMUNITY.--In addition to its mechanical defenses against disease, the body shows a varying degree of _immunity_, or the power possessed by living organisms to resist infections. Immunity or resistance is the opposite of susceptibility. It is exceedingly variable, being greater or less in different people and under different conditions, but the exact ways in which it is brought about are still in many cases far from clear.

Immunity may be _natural_ or _acquired_. By natural immunity is meant an inherited characteristic by which all individuals of a species are immune to a certain disease. The natural immunity of certain species of animals to the diseases of other animals is well known. Man is immune to many diseases of lower animals, and they in turn are immune to many diseases of man. Cattle, for instance, are immune to typhoid and yellow fever, while man shows high resistance to rinderpest and Texas fever; both, however, are susceptible to tuberculosis, to which goats are immune. There are all gradations of immunity within the same species. Moreover, certain individuals have a personal immunity against diseases to which others of the same race or species are susceptible.

Immunity may be _acquired_ in several ways. It is commonly known that one attack of certain communicable diseases renders the individual immune for a varying length of time, and sometimes for life. Among these diseases are smallpox, measles, whooping-cough, scarlet fever, infantile paralysis, typhoid fever, chicken-pox, and mumps; erysipelas and pneumonia on the other hand appear to diminish resistance and to leave a person more susceptible to later attacks.

Again, in some cases immunity may be artificially acquired by introducing certain substances into the body to increase its resistance. Examples of this method include the use of antitoxin as a protection against diphtheria, of sera in pneumonia and other infections, and vaccination against smallpox and typhoid fever whereby a slight form of the disease is artificially induced. Laboratory research goes on constantly, and doubtless many more substances will eventually be discovered that will reduce human misery as vaccines and antitoxin have already reduced it.

Vaccination and inoculation have saved thousands of lives. Smallpox, once more prevalent than measles, was the scourge of Europe until vaccination was introduced. During the 18th century it was estimated that 60,000,000 people died of it, and at the beginning of the 19th century one-fifth of all children born died of smallpox before they were 10 years old. In countries where vaccination is not practised the disease is as serious as ever; in Russia during the five years from 1893-97, 275,502 persons died of smallpox, while in Germany where vaccination is compulsory, only 8 people died of it during the year 1897. Death rates from diphtheria and typhoid fever have been greatly reduced by the use of antitoxin and antityphoid vaccine. Thus in New York State in 1894, before antitoxin was generally used, 99 out of every 100,000 of the population died of diphtheria, while only 20 out of 100,000 died of it in 1914. In 1911 a United States Army Division of more than 12,000 men camped at San Antonio, Texas, for four months. All of these men were vaccinated against typhoid fever and only a single case occurred during the summer, although conditions of camp life always tend to spread the disease.

While many and various factors tend to lower resistance rather than to increase it, the idea that these factors act equally in all kinds of infection is erroneous.

"The principal causes which diminish resistance to infection are: wet and cold, fatigue, insufficient or unsuitable food, vitiated atmosphere, insufficient sleep and rest, worry, and excesses of all kinds. The mechanism by which these varying conditions lower our immunity must receive our attention, for they are of the greatest importance in preventive medicine. It is a matter of common observation that exposure to wet and cold or sudden changes of temperature, overwork, worry, stale air, poor food, etc., make us more liable to contract certain diseases. The tuberculosis propaganda that has been spread broadcast with such energy and good effect has taught the value of fresh air and sunshine, good food, and rest in increasing our resistance to this infection.

"There is, however, a wrong impression abroad that because a lowering of the general vitality favors certain diseases, such as tuberculosis, common colds, pneumonia, septic and other infections, it plays a similar rôle in all communicable diseases. Many infections, such as smallpox, measles, yellow fever, tetanus, whooping-cough, typhoid fever, cholera, plague, scarlet fever, and other diseases, have no particular relation whatever to bodily vigor. These diseases often strike down the young and vigorous in the prime of life. The most robust will succumb quickly to tuberculosis if he receives a sufficient dose of the virulent micro-organisms. A good physical condition does not always temper the virulence of the disease; on the contrary, many infections run a particularly severe course in strong and healthy subjects, and, contrariwise, may be mild and benign in the feeble. Physical weakness, therefore, is not necessarily synonymous with increased susceptibility to all infections, although true for some of them. In other words, 'general debility' lowers resistance in a specific, rather than in a general, sense."--(Rosenau: Preventive Medicine and Hygiene, pp. 403 and 404.)

CARRIERS

Well persons who carry in their bodies pathogenic germs but who themselves have no symptoms of disease are called carriers. Thus typhoid carriers have typhoid bacilli in the intestinal tract, while they themselves show no symptoms of typhoid fever; diphtheria carriers have bacilli of diphtheria in the throat or nose, but have themselves no symptoms of diphtheria, and so on. It has now been proved that many patients harbor bacteria for weeks, months, or even years following an infection, and are dangerous distributors of disease; also, some healthy individuals without a history of illness harbor living bacteria which may infect susceptible persons in the usual ways. Transmission by healthy carriers goes far to explain the occurrence of diseases among persons who have apparently not been exposed. This explanation has greatly clarified the whole problem of the spread of communicable diseases. Carriers, unfortunately, exist in large numbers, and render the ultimate control of disease exceedingly difficult. They can usually be identified by bacteriological tests. To some extent they can be supervised; food handlers at least should be legally obliged to submit to physical examinations, and should be licensed only when proved free from communicable disease.

Diseases are also spread by persons suffering from them in a form so mild or so unusual that they pass unrecognized. These persons are known as "missed" cases. Carriers of disease and "missed" cases go freely about the community, handling food, using common drinking cups, travelling in crowded street cars, standing in crowded shops; in various ways coming into close contact with other people, coughing and sneezing and kissing their friends no less often than normal individuals. It is consequently clear that the bodily discharges of supposedly normal persons may be hardly less a menace than those of persons known to be infected.

Diseases that depend for transmission upon milk, water, food, and insects may be controlled by public action, that is, by specific measures taken by a large group of people in order to protect the individual. Such action constitutes _public sanitation_. There is, however, a large group of diseases, chiefly sputum-borne, that cannot be controlled except by individual action. Such individual action constitutes a large part of _personal hygiene_.

The whole problem of controlling infections sounds simple, depending as it does for the most part upon unpolluted water, milk, and food, extermination of certain insects, and cleanliness in personal behaviour. In practice the problem is not so easy. Public sanitation has performed miracles in the past, and will do much in the future; behaviour, however, will continue to be influenced by many factors, social and economic as well as personal. Ignorance of the laws of health is an obstacle to progress, but in modern conditions even the instructed may be unable to control their ways of living and working. Indeed, such control is at present limited to the privileged few. On the ignorant and the poor, those least able to bear it, society loads the heaviest burden of sickness. Only when ignorance and poverty are abolished, as one day they will be, can the final stage be reached in the fight for public health.

THE NON-COMMUNICABLE DISEASES

In this group is included a great variety of maladies. Of some the causes are known, while in the case of others, origin, prevention, and remedy are still obscure. Here belong defects in structure of the body, both hereditary and acquired; insanity and other nervous diseases; new growths, like tumors and cancer; disturbances of bodily processes, as malnutrition and gout; and the important class of degenerative diseases, like arteriosclerosis, in which tissues become hardened and fibrous and hence less able to perform their normal functions.

The degenerative diseases are playing a menacing part in national health. The average length of life in the United States has shown a marked increase it is true, during the last 40 years. But this gain represents chiefly the saving of life through prevention of communicable diseases, especially among babies and children; among people who have passed the 30th year on the other hand, death rates are actually increasing. This increase is most marked after the age of 45, and is caused chiefly by the increase of cancer, and of degenerative diseases of the heart, blood vessels, and kidneys. Degeneration of tissues is normally a condition typical of old age, and in aged persons it may occur in any tissue. There is no elixir of youth, and for old age there is no cure. But the important facts in this connection are that degenerative changes now occur prematurely, and that among a vast number of people, in various classes of society and various occupations, the vital organs show a marked tendency to break down after the age of 45.

This condition is not inevitable. Before the beginning of the present war, death rates at all ages were decreasing in England, Sweden, and other European countries. In America also degenerative diseases can be checked or prevented to a large extent, and it is highly important that their causes should be generally understood.

The two groups following include some of the probable causes:

1. Conditions of life which result in continued overwork, and mental overwork in particular; worry, excitement, insufficient recreation and exercise, and other kinds of nervous strain typical of modern life, especially in cities.

2. Irritating substances in the body, including poisonous substances resulting from infectious diseases, and from syphilis in particular; poisons from chronic infections, alcohol, and industrial poisons such as lead and other metals; overeating and improper eating, especially of meat and other proteins, and rich or highly seasoned food; faulty digestion, constipation, and imperfect elimination through the kidneys.--(See Dr. A. E. Shipley, in bulletin of the N. Y. City Dept. of Health, Feb., 1915.)

The importance of early recognition cannot be overemphasized. In many of these troubles the symptoms are not pronounced, and the victims have no knowledge of their condition until they happen to be examined for life insurance, or until the disease is far advanced. And even when they realize that trouble exists, as for example constipation or overwork, most people absolutely fail to realize how serious the consequences may be. The first step toward remedy is periodic complete physical examination by a competent physician, in order to learn in time how to prevent these degenerative diseases, if present, from growing worse. The custom of undergoing an annual physical examination is becoming more common, and "such a course, conservatively estimated, would add 5 years to the average life of persons between 45 and 50."--(Winslow.)

"Recently, we have been making examinations of the employees of whole institutions, large banks and other industrial concerns in New York City, and we find almost the same conditions there. Out of 2000 such examinations among young men and women of an average age of 33, just in the early prime of life, men and women supposedly picked because of their especial fitness for work, only 3.14% were found free of impairment or of habits of living which are obviously leading to impairment. Of the remaining persons, 96.69% were unaware of impairment; 5.38% of the total number examined were affected with chronic heart trouble; 13.10% with arteriosclerosis; 25.81% with high or low blood pressure; 35.65% with sugar, casts or albumen in the urine; 12.77% with combination of both heart and kidney disease; 22.22% with decayed teeth or infected gums; 16.03% with faulty vision uncorrected.... The fact of greatest import, however, was that impairment, sufficiently serious to justify the examiner in referring the examinee to his family physician for medical treatment, was found in 59% of the total number of cases, while 37.86% were on the road to impairment because of the use of "too much alcohol," or "too much tobacco," constipation, eye-strain, overweight, diseased mouths, errors of diet, and so forth....

"And what is the cause of this appalling increase, in the United States, of these and other degenerative diseases? I believe it can be shown to the satisfaction of any reasonable person that the increase is largely due to the neglect of individual hygiene in United States....

"If a man were suddenly afflicted with smallpox or typhoid fever or any other acute malady, he would lose no time in getting expert advice and applying every known means to save his life. But his life may be threatened just as seriously, though possibly not so imminently, by arteriosclerosis, heart disease, or Bright's disease, and he will do nothing to prevent the encroachment of these diseases until it is too late, but will continue to eat as he pleases, drink as he pleases, smoke as he pleases, or overwork, and worry himself into a premature grave."--("Conservation of Life at Middle Age," Prof. Irving Fisher, Am. Journal of Public Health, July, 1915.)

Periodic physical examinations are as necessary for children as for adults, in order to detect physical defects. These defects are known to have such an immense bearing upon health that routine examinations of all children have become an integral part of the work of enlightened public schools.

Prevention of degenerative disease, then, as well as of the enormous numbers of preventable accidents and injuries, depends in large measure upon proper living conditions and proper personal habits. The infectious diseases, according to Dr. Hill, cost us annually at least 10 billion dollars in addition to the loss of life, and he adds: "The infectious diseases in general radiate from and are kept going by women."--(Hill-- New Public Health, p. 30.) Women, it is true, can prevent many of the infections, but they can do still more, for hygienic habits to be effective must be acquired early, and mothers and teachers, because they have practically the entire control of children, have the power to prevent many cases of degenerative as well as of communicable disease.

EXERCISES

1. Distinguish between communicable and non-communicable disease.

2. Describe the part played by micro-organisms in causing disease.

3. Describe the structure of bacteria and their method of multiplication.

4. In what ways are pathogenic germs transmitted from person to person?

5. Upon what preventive measures does the control of communicable diseases depend?

6. What is meant by immunity?

7. Against what diseases may immunity be acquired artificially? How has the practice of immunizing affected death rates from communicable diseases?

8. What factors tend to lower resistance? Do they act equally in the case of all diseases?

9. Define a carrier, and explain the importance of carriers in the spread of disease.

10. Name some of the characteristics and causes of degenerative diseases.

11. Whom do the degenerative diseases most commonly affect?

12. Describe methods that should be employed to prevent degenerative diseases.

FOR FURTHER READING

The New Public Health--Hill, Chapters I-IX.

Health and Disease--Roger I. Lee, Chapters XV-XXIV.

Principles of Sanitary Science and the Public Health--Sedgwick, Chapters I, II, III.

Scientific Features of Modern Medicine--Frederic S. Lee, Chapters II, IV-VI.

Disease and Its Causes--Councilman, Chapter I.

Preventive Medicine and Hygiene--Rosenau.

Publications of the Life Extension Institute--25 West 45th Street, New York City.