Physiologists have recognized for a long time that stuffiness in a close atmosphere is not due to diminution of oxygen or excess of carbon dioxide in the air breathed, or to any other impurity in the air. Such feelings are now shown to be due to the effect of longer infra-red rays on the skin, and are accompanied by a reflex narrowing of the air-ways of the nose and lungs. These effects are set aside by cool air acting on the skin and in many people also by shorter infra-red rays from bright sources of heat. This is why some people are much more comfortable with a bright source of heat than with a dark or dull red one. When people go out of doors to get a “breather”, or stand before an open window during physical exercises, they are instinctively using the stimulus of cold to widen their air-tubes. In open air treatment, and when sleeping with an open window, the same effect is obtained.

All rooms should be adequately ventilated with cool air to prevent stuffy feelings, and keep the air-ways open. Such ventilation will, at the same time, sweep away infection spread by “carriers”.

Partial obstruction of the air-tubes hinders the passage of blood through the lungs; it is this which causes failure of breathing when the obstruction is considerable.

Bleeding is of value because it relieves to a certain extent the impeded circulation.

Breathing through a narrow tube can be used as a test of fitness. An airway gauge has been designed for making such a test.