This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
To bathe before breakfast is the custom of some robust persons, but is never free from risk, and sometimes seriously injures weakly subjects: for after the long fast of night the circulatory and central nervous organs are more liable to depression from sudden shock or over-fatigue. On the other hand, to bathe soon after a meal arrests the process of digestion, and may give rise to very unpleasant gastric and cerebral symptoms. The best results are obtained from bathing two or three hours after the early morning meal, when the stomach is nearly empty, and there should be at least a brief interval of rest or of but moderate exercise, according to the weather, between the bath and the following meal. The object aimed at being a marked and prolonged reaction, this is best obtained from a bath taken during a condition of the greatest nutritive and functional activity, when the work of the stomach is over and the blood is enriched by the products of digestion.