ABSTRACT
The source of almost all the energy developed in the human body is the combination of food with oxygen. People can replace one kind of food by another, but oxygen cannot be replaced. The combination occurs in all the tissues, and both food and oxygen must be supplied to them by the blood. All organs are sooner or later damaged by want of oxygen, but the brain is by far the most sensitive. Oxygen may be cut off suddenly from the tissues by such means as drowning, strangling, or beheading, but the physiologist, psychologist, and doctor find more to interest them in the effects of partial but prolonged shortage. This generally arises in one of three ways: shortage of oxygen in the air, interference with its passage through the lung membrane into the blood, or failure of the blood to carry it to the tissues. The oxygen in blood is mostly combined with haemoglobin, which gives it its red colour.
