This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
The action of drugs is altered by the changes in temperature due to the seasons. Galen supposed that the quantity of blood in the body was increased in spring, and in this country, till within recent years, it was a common custom for people to be regularly bled every spring. Purgatives were not unfrequently administered also at the same time. There are, no doubt, changes corresponding with the seasons in the human organisation, although these are better marked in the lower animals; e.g. deer, in which the antlers bud regularly in spring and reach perfection just at the breeding season. It is possible that the abolition of the practice of bleeding in spring and the changes in other plans of treatment formerly adopted, may not be altogether due, as some suppose, to increased knowledge on our part, but rather to the occurrence of a change of type not only in diseases but also in slight ailments, and to the need for such treatment having disappeared. Formerly, before the introduction of coaches, and still more of railways, locomotion was difficult and transportation was expensive; in consequence of this, the food consumed by the generality of people was different in character, loaf bread being very little used, and salt meat often used for weeks and months together during the winter with comparatively few vegetables. Such a diet might naturally lead to a condition of body which would be benefited by bleeding and purgatives.