Oak Apple day (May 29th) is called in Hampshire "Shikshak" day.
The bark of an oak tree, and the galls, or apples, produced on its leaves, or twigs, by an insect named cynips, are very astringent, by reason of the gallo-tannic acid which they furnish abundantly. This acid, given as a drug, or the strong decoction of oak bark which contains it, will serve to restrain bleedings if taken internally; and finely powdered oak bark, when inhaled pretty frequently, has proved very beneficial against consumption of the lungs in its early stages. Working tanners are well known to be particularly exempt from this disease, probably through their constantly inhaling the peculiar aroma given off from the tan pits; and a like effect may be produced by using as snuff the fresh oak bark dried and reduced to an impalpable powder, or by inhaling day after day the steam given off from recent oak bark infused in boiling water.
Marble galls are formed on the back of young twigs, artichoke galls at their extremities, and currant galls by spangles on the under surface of the leaves. From these spangles females presently emerge, and lay their eggs on the catkins, giving rise to the round shining currant galls.
Source: Herbal Simples Approved for Modern Uses of Cure, William Thomas Fernie