A person has a temperature of 40° C. Should he see a physician?

Not necessarly (but you should pay attention)

Explanation:

A normal temperature for a resting, healthy adult is about 37°C. It can vary around 1 or 2 degrees up or down throughout the day.

Fever is a way that our body has to fight disease, as some of the disease-causing organisms cannot tolerate higher temperatures.

At 40°C, it is considered a fever, however, it doesn't necessarily mean you have to go to the doctor, as body temperatures usually return to normal when the illness goes away, for example, with a regular cold. However if the fever lasts for more than a couple of days, the temperature keeps going up, or other symptoms appear, it is highly recommended that you see a doctor.