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The Purkinje effect or Purkinje phenomenon (Czech: [ˈpurkɪɲɛ] (listen); sometimes called the Purkinje shift, often incorrectly pronounced ) is the tendency for the peak luminance sensitivity of the eye to shift toward the blue end of the color spectrum at low illumination levels as part of dark adaptation. In consequence, reds will appear darker relative to other colors as light levels decrease. The effect is named after the Czech anatomist Jan Evangelista Purkyně. While the effect is often described from the perspective of the human eye, it is well established in a number of animals under the same name to describe the general shifting of spectral sensitivity due to pooling of rod and cone output signals as a part of dark/light adaptation.

This effect introduces a difference in color contrast under different levels of illumination. For instance, in bright sunlight, geranium flowers appear bright red against the dull green of their leaves, or adjacent blue flowers, but in the same scene viewed at dusk, the contrast is reversed, with the red petals appearing a dark red or black, and the leaves and blue petals appearing relatively bright.

The sensitivity to light in scotopic vision varies with wavelength, though the perception is essentially black-and-white. The Purkinje shift is the relation between the absorption maximum of rhodopsin, reaching a maximum at about 500 nanometres (2.0×10⁻⁵ in), and that of the opsins in the longer-wavelength cones that dominate in photopic vision, about 555 nanometres (2.19×10⁻⁵ in) (green).

In visual astronomy, the Purkinje shift can affect visual estimates of variable stars when using comparison stars of different colors, especially if one of the stars is red.

Clanging (or clang associations) is a symptom of mental disorders, primarily found in patients with schizophrenia and bipolar disorder. This symptom is also referred to as association chaining, and sometimes, glossomania.

Steuber defines it as "repeating chains of words that are associated semantically or phonetically with no relevant context". This may include compulsive rhyming or alliteration without apparent logical connection between words.

Clanging refers specifically to behavior that is situationally inappropriate. While a poet rhyming is not evidence of mental illness, disorganized speech that impedes the patient's ability to communicate is a disorder in itself, often seen in schizophrenia.

Min Chiu Li (Chinese: 李敏求; pinyin: Lǐ Mǐnqiú; 1919–1980) was a Chinese-American oncologist and cancer researcher. Li was the first scientist to use chemotherapy to cure widely metastatic, malignant cancer.

Elixir sulfanilamide was an improperly prepared sulfonamide antibiotic that caused mass poisoning in the United States in 1937. It is believed to have killed more than 100 people. The public outcry caused by this incident and other similar disasters led to the passing of the 1938 Federal Food, Drug, and Cosmetic Act, which significantly increased the Food and Drug Administration's powers to regulate drugs.

Gustav III of Sweden's coffee experiment was a twin study ordered by the king to study the health effects of coffee. Although the authenticity of the event has been questioned, the experiment, which was conducted in the second half of the 18th century, failed to prove that coffee was a dangerous beverage.

RICE is a mnemonic acronym for the four elements of a treatment regimen that was once recommended for soft tissue injuries: rest, ice, compression, and elevation. It was considered a first-aid treatment rather than a cure and aimed to control inflammation. It was thought that the reduction in pain and swelling that occurred as a result of decreased inflammation helped with healing. The protocol was often used to treat sprains, strains, cuts, bruises, and other similar injuries. Ice has been used for injuries since at least the 1960s, in a case where a 12-year-old boy needed to have a limb reattached. The limb was preserved before surgery by using ice. As news of the successful operation spread, the use of ice to treat acute injuries became common.

The mnemonic was introduced by Dr. Gabe Mirkin in 1978. He withdrew his support of this regimen in 2014 after learning of the role of inflammation in the healing process. The implementation of RICE for soft tissue injuries as described by Dr. Mirkin is no longer recommended, as there is not enough research on the efficacy of RICE in the promotion of healing. In fact, many components of the protocol have since been shown to impair or delay healing by inhibiting inflammation. Early rehabilitation is now the recommendation to promote healing. Ice, compression, and elevation may have roles in decreasing swelling and pain, but have not shown to help with healing an injury.

There are different variations of the protocol, which may emphasize additional protective actions. However, these variations similarly lack sufficient evidence to be broadly recommended. Examples include PRICE, POLICE, and PEACE & LOVE.

Scottish man Angus Barbieri (1939 – 7 September 1990) fasted for 382 days, from June 1965 to July 1966. He lived on tea, coffee, soda water, and vitamins while living at home in Tayport, Scotland, and frequently visiting Maryfield Hospital for medical evaluation. He lost 276 pounds (125 kg) and set a record for the length of a fast.

Herd immunity (also called herd effect, community immunity, population immunity, or social immunity) is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, whether through previous infections or vaccination, thereby providing a measure of protection for individuals who are not immune. In a population in which a large proportion of individuals possess immunity, such people being unlikely to contribute to disease transmission, chains of infection are more likely to be disrupted, which either stops or slows the spread of disease. The greater the proportion of immune individuals in a community, the smaller the probability that non-immune individuals will come into contact with an infectious individual, helping to shield non-immune individuals from infection.

Individuals can become immune by recovering from an earlier infection or through vaccination. Some individuals cannot become immune due to medical reasons, such as an immunodeficiency or immunosuppression, and in this group herd immunity is a crucial method of protection. Once a certain threshold has been reached, herd immunity gradually eliminates a disease from a population. This elimination, if achieved worldwide, may result in the permanent reduction in the number of infections to zero, called eradication. Herd immunity created via vaccination contributed to the eventual eradication of smallpox in 1977 and has contributed to the reduction of the frequencies of other diseases. Herd immunity does not apply to all diseases, just those that are contagious, meaning that they can be transmitted from one individual to another. Tetanus, for example, is infectious but not contagious, so herd immunity does not apply.

The term "herd immunity" was first used in 1923. It was recognized as a naturally occurring phenomenon in the 1930s when it was observed that after a significant number of children had become immune to measles, the number of new infections temporarily decreased, including among susceptible children. Mass vaccination to induce herd immunity has since become common and proved successful in preventing the spread of many infectious diseases. Opposition to vaccination has posed a challenge to herd immunity, allowing preventable diseases to persist in or return to communities that have inadequate vaccination rates.

Liquid breathing is a form of respiration in which a normally air-breathing organism breathes an oxygen-rich liquid (such as a perfluorocarbon), rather than breathing air.

This requires certain physical properties such as respiratory gas solubility, density, viscosity, vapor pressure, and lipid solubility which some, but not all, perfluorochemicals (perfluorocarbon) have. Thus, it is critical to choose the appropriate PFC for a specific biomedical application, such as liquid ventilation, drug delivery or blood substitutes. The physical properties of PFC liquids vary substantially; however, the one common property is their high solubility for respiratory gases. In fact, these liquids carry more oxygen and carbon dioxide than blood.

In theory, liquid breathing could assist in the treatment of patients with severe pulmonary or cardiac trauma, especially in pediatric cases. Liquid breathing has also been proposed for use in deep diving and space travel. Despite some recent advances in liquid ventilation, a standard mode of application has not yet been established.

This article is a list of deaths caused by an infectious disease. Widespread non-communicable diseases such as cardiovascular disease and cancer are not included.