Below approximately 77 degrees Fahrenheit (25 degrees Celsius), the heart may stop entirely — what is called cardiac arrest.

Below approximately 68 degrees Fahrenheit (20 degrees Celsius), the brain effectively ceases functioning in any meaningful way.

At every stage of this progression, the critical variable is: has cellular damage occurred that cannot be reversed?

This is the key question for Jean Hilliard’s case.

The conventional wisdom in medicine, and the empirical observation that had been made in cases of hypothermia long before 1980, is that the slowing of metabolism that accompanies hypothermia can protect cells and organs from the damage that would otherwise result from inadequate oxygen supply and from the disruption of normal cellular chemistry.

The cold buys time.