Human Disease, in medicine, any harmful change that interferes with the normal appearance, structure, or function of the body or any of its parts. Since time immemorial, disease has played a role in the history of societies. It has affected-and been affected by-economic conditions, wars, and natural disasters. Indeed, the impact of disease can be far greater than better-known calamities. An epidemic of influenza that swept the globe in 1918 killed between 20 million and 40 million people.　　Diseases have diverse causes, which can be classified into two broad groups: infectious and noninfectious. Infectious diseases can spread from one person to another and are caused by microscopic organisms that invade the body. Noninfectious diseases are not communicated from person to person and do not have, or are not known to involve, infectious agents. Some diseases, such as the common cold, are acute, coming on suddenly and lasting for no more than a few weeks. Other diseases, such as arthritis（關(guān)節(jié)炎）, are chronic, persisting for months or years, or recurring frequently.　　聽力　　Every disease has certain characteristic effects on the body. Some of these effects, called symptoms and signs, include fever, inflammation（發(fā)炎）, pain, fatigue（疲勞）, dizziness（頭暈）, nausea（惡心）, and rashes（皮疹）, and are readily apparent to the patient. These symptoms offer important clues that help physicians and other health care professionals make a diagnosis（診斷）. Many times, however, the symptoms point to several possible disorders. In those cases, doctors rely on medical tests, such as blood examinations and X rays, to confirm the diagnosis.　　The course of a disease-that is, the path it follows from onset to end-can vary tremendously, depending largely on the individual and the treatment he or she receives. For example, otherwise healthy people usually recover quickly from a bout of pneumonia if given proper treatment, whereas pneumonia often proves fatal to people with a weakened immune system and to those who do not receive prompt, effective treatment.　　Preventing the Diseases（疾病預(yù)防）　　It is much less costly, in terms of both human suffering and economics, to prevent disease than to treat it. Public health services and medical professionals play critical roles in helping people avoid disease. In addition, each individual plays a vital role in protecting his or her personal health.　　Public health services are charged with protecting community health. Their activities include provision of adequate clean water and the sanitary disposal of sewage and other wastes.　　Physicians, dentists, and other medical experts have a number of preventive tools at their disposal. Among the most effective are vaccines（注射疫苗）, which stimulate the immune system to produce antibodies against particular antigens.　　Regular medical check-ups are another important preventive tool. These help doctors to find disease in its early stages, when it is easier to treat and before it causes significant damage.　　Even the finest public health and medical services are of limited value to people who have poor health habits. Numerous studies have proven that physical health and longevity are linked to the following: eating a balanced diet, maintaining proper weight, exercising regularly, avoiding tobacco, and avoiding alcohol or consuming it in moderation. People who fail to follow these guidelines increase their risk of cardiovascular disease, cancer, hepatitis（肝炎）, and other lethal diseases（致命疾?。?　　Life Span（壽命）　　At the beginning of the 20th century, people in the United States had an average life span of about 50 years. By the time the century neared its close, average life span had risen to 76 years. Other developed countries experienced similar increases. Much of the credit for these longer life spans-and for the good health that accompanies them-is due to the conquering of diseases, thanks to vaccines, antibiotics, sophisticated surgical tools, and other medical miracles. The challenges ahead include bringing the benefits of this medical knowledge to all peoples of the world, and expanding on current knowledge in order to understand, treat, and prevent the diseases that still confront us.　　Influenza（流感）　　Influenza is an acute disease with a rapid onset and pronounced symptoms. After the influenza virus invades a persons body, an incubation period of one to two days passes before symptoms appear. Classic symptoms include sore throat, dry cough, stuffed or runny nose, chills, fever with temperatures as high as 39? C （103? F）, aching muscles and joints, headache, loss of appetite, occasional nausea and vomiting, and fatigue. For most people flu symptoms begin to subside after two to three days and disappear in seven to ten days. However, coughing and fatigue may persist for two or more weeks.　　Breathing Problems（呼吸疾病）, diseases or conditions affecting respiration, usually caused by cigarette smoke or other pollutants, allergies, or an inherited trait.　　Diarrhea（腹瀉）, frequent passage of abnormally loose, watery stool. Diarrhea usually develops suddenly and may last from several hours to a few days. It is often accompanied by abdominal pains, low fever, nausea, and vomiting. Diarrhea is not a disease. It is a symptom of numerous disorders, such as food poisoning from contaminated foods or beverages, infections by viruses and bacteria, or anxiety. The usual treatment for diarrhea consists of bed rest, drinking liquids to replace fluids and salts lost from the body, and eating soft foods.　　Severe mental illness （精神疾?。゛lmost always alters a persons life dramatically. People with severe mental illnesses experience disturbing symptoms that can make it difficult to hold a job, go to school, relate to others, or cope with ordinary life demands. Some individuals require hospitalization because they become unable to care for themselves or because they are at risk of committing suicide.

　　Human Disease, in medicine, any harmful change that interferes with the normal appearance, structure, or function of the body or any of its parts. Since time immemorial, disease has played a role in the history of societies. It has affected-and been affected by-economic conditions, wars, and natural disasters. Indeed, the impact of disease can be far greater than better-known calamities. An epidemic of influenza that swept the globe in 1918 killed between 20 million and 40 million people.　　Diseases have diverse causes, which can be classified into two broad groups: infectious and noninfectious. Infectious diseases can spread from one person to another and are caused by microscopic organisms that invade the body. Noninfectious diseases are not communicated from person to person and do not have, or are not known to involve, infectious agents. Some diseases, such as the common cold, are acute, coming on suddenly and lasting for no more than a few weeks. Other diseases, such as arthritis（關(guān)節(jié)炎）, are chronic, persisting for months or years, or recurring frequently.　　聽力　　Every disease has certain characteristic effects on the body. Some of these effects, called symptoms and signs, include fever, inflammation（發(fā)炎）, pain, fatigue（疲勞）, dizziness（頭暈）, nausea（惡心）, and rashes（皮疹）, and are readily apparent to the patient. These symptoms offer important clues that help physicians and other health care professionals make a diagnosis（診斷）. Many times, however, the symptoms point to several possible disorders. In those cases, doctors rely on medical tests, such as blood examinations and X rays, to confirm the diagnosis.　　The course of a disease-that is, the path it follows from onset to end-can vary tremendously, depending largely on the individual and the treatment he or she receives. For example, otherwise healthy people usually recover quickly from a bout of pneumonia if given proper treatment, whereas pneumonia often proves fatal to people with a weakened immune system and to those who do not receive prompt, effective treatment.　　Preventing the Diseases（疾病預(yù)防）　　It is much less costly, in terms of both human suffering and economics, to prevent disease than to treat it. Public health services and medical professionals play critical roles in helping people avoid disease. In addition, each individual plays a vital role in protecting his or her personal health.　　Public health services are charged with protecting community health. Their activities include provision of adequate clean water and the sanitary disposal of sewage and other wastes.　　Physicians, dentists, and other medical experts have a number of preventive tools at their disposal. Among the most effective are vaccines（注射疫苗）, which stimulate the immune system to produce antibodies against particular antigens.　　Regular medical check-ups are another important preventive tool. These help doctors to find disease in its early stages, when it is easier to treat and before it causes significant damage.　　Even the finest public health and medical services are of limited value to people who have poor health habits. Numerous studies have proven that physical health and longevity are linked to the following: eating a balanced diet, maintaining proper weight, exercising regularly, avoiding tobacco, and avoiding alcohol or consuming it in moderation. People who fail to follow these guidelines increase their risk of cardiovascular disease, cancer, hepatitis（肝炎）, and other lethal diseases（致命疾?。?　　Life Span（壽命）　　At the beginning of the 20th century, people in the United States had an average life span of about 50 years. By the time the century neared its close, average life span had risen to 76 years. Other developed countries experienced similar increases. Much of the credit for these longer life spans-and for the good health that accompanies them-is due to the conquering of diseases, thanks to vaccines, antibiotics, sophisticated surgical tools, and other medical miracles. The challenges ahead include bringing the benefits of this medical knowledge to all peoples of the world, and expanding on current knowledge in order to understand, treat, and prevent the diseases that still confront us.　　Influenza（流感）　　Influenza is an acute disease with a rapid onset and pronounced symptoms. After the influenza virus invades a persons body, an incubation period of one to two days passes before symptoms appear. Classic symptoms include sore throat, dry cough, stuffed or runny nose, chills, fever with temperatures as high as 39? C （103? F）, aching muscles and joints, headache, loss of appetite, occasional nausea and vomiting, and fatigue. For most people flu symptoms begin to subside after two to three days and disappear in seven to ten days. However, coughing and fatigue may persist for two or more weeks.　　Breathing Problems（呼吸疾?。? diseases or conditions affecting respiration, usually caused by cigarette smoke or other pollutants, allergies, or an inherited trait.　　Diarrhea（腹瀉）, frequent passage of abnormally loose, watery stool. Diarrhea usually develops suddenly and may last from several hours to a few days. It is often accompanied by abdominal pains, low fever, nausea, and vomiting. Diarrhea is not a disease. It is a symptom of numerous disorders, such as food poisoning from contaminated foods or beverages, infections by viruses and bacteria, or anxiety. The usual treatment for diarrhea consists of bed rest, drinking liquids to replace fluids and salts lost from the body, and eating soft foods.　　Severe mental illness （精神疾?。゛lmost always alters a persons life dramatically. People with severe mental illnesses experience disturbing symptoms that can make it difficult to hold a job, go to school, relate to others, or cope with ordinary life demands. Some individuals require hospitalization because they become unable to care for themselves or because they are at risk of committing suicide.