The limitations of that approach don't line up with the example. Someone running a fever is running a fever because of an immune response to illness a lot of th

The limitations of that approach don't line up with the example. Someone running a fever is running a fever because of an immune response to illness a lot of the time, which is an aggregate response. The body has trillions of cells, in the case of temperature you don't need a reading of each one. Researchers sometimes do, and medical testing of methods, drugs, or devices is a lot more scrutinized before doctors ever get access.