This principle — that cold protects biology, at least temporarily — is what underpins the medical dictum that Sather applied to Jean Hilliard: “No one is dead until they are warm and dead.”

The question is where the protection ends and the damage begins.

Cold protects cells from the effects of inadequate oxygen supply.

But cold also, at sufficient temperatures, causes direct physical damage to cells — particularly through the formation of ice crystals inside and between cells, which ruptures cell membranes and destroys the cellular structure.

Jean Hilliard’s survival, to the extent that it can be explained, rests on a distinction that is more subtle than it might appear from the outside: the distinction between surface freezing and core freezing.

The Surface Versus The Core