Human body temperature to give the most accurate assessment of core body temperature, particularly in hypothermia. In the early 2000s, ingestible thermistors in capsule form were produced, allowing the temperature inside the digestive tract to be transmitted to an external receiver; one study found that these were comparable in accuracy to rectal temperature measurement. In the 19th century, most books quoted "blood heat" as 98 °F, until a study published the mean (but not the variance) of a large sample as . Subsequently that mean was widely quoted as "37 °C or 98.4 °F" until editors realised 37 °C is closer to 98.6
Body piercing materials some flexibility of the material is desired. PTFE is commonly used as a retainer. Acrylic, sold as Plexiglas or any of a variety of names, is a transparent plastic, in piercing mostly used for plugs and tapers. Due to the material's smoothness, it has been used for stretching. Many overenthusiastic wearers have damaged their holes with acrylic tapers. It is not a safe material for damaged or new piercings and can not be heat sterilized by autoclave as it can melt or discolor. Acrylics can emit carcinogenic toxins above 70 degrees, which is above normal body temperature. Italso a fragile