This section is from the "Nature Cure: Philosophy and Practice Based on the Unity of Disease and Cure" book, by Henry Lindlahr.
Even among the adherents of Nature Cure there are those who think that air and light baths should be taken out of doors in warm weather only and in winter time only in well-heated rooms.
This is a mistake. The effect of the air bath upon the organism is subject to the same Law of Action and Reaction which governs the effects of water applications.
If the temperature of air or water is the same or nearly the same as that of the body, no reaction takes place, the conditions within the system remain the same. But if the temperature of air or water is considerably lower than the body temperature there will be a reaction.
In order to react against the chilling effect of cold air or water, the nerve centers which control the circulation send the blood to the surface in large quantities, flushing the skin with warm, red, arterial blood. The flow of the blood stream is greatly accelerated, and the elimination of morbid matter on the surface of the body is correspondingly increased.