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
Wilson's temperature syndrome to man." He also says that it is "the most common of all chronic ailments and probably takes a greater toll on society than any other medical condition." Wilson says that low thyroid symptoms and low temperatures in the presence of normal thyroid function tests are not due to hypothyroidism, and might be reversed with a few months of treatment. To distinguish this condition from hypothyroidism, he named it Wilson's (temperature) syndrome. He states that it is "especially brought on by stress" and can persist after the stress has passed. He says that the main diagnostic sign is a body