Hypothermia is the body's last defense against cold, its final effort to defend the vital organs.

The pulse rate slows and blood is shunted to the critical organs and away from the extremities. The effect is to keep the heart and lungs working at the expense of the hands, feet and head.

The problem is that in many situations the hypothermia victim needs the use of his extremities, to hang on to a floating canoe or keep walking to shelter. The blood shortage also affects the brain, and most survivors of hypothermia recall a feeling of well-being sweeping over them as they began to lose their mental grip.

According to John Lentz, who survived a near-fatal drift in frigid waters of the Northwest Territories some years back, one of the most frightening times came after his rescue.

He was stripped, wrapped in a sleeping bag and tucked away into a tent. Suddenly his body began shaking with convulsions, which continued for several minutes. He couldn't breathe.

Lentz learned later that it was a common problem, but the people who treated him didn't know about it. The ideal solution is to strip the victim and sandwich him naked in a sleeping bag between two other warm naked human bodies, Lentz said.

That way the victim can steal body heat and recover.