The action of tannic acid is strictly local, and depends upon its power of precipitating albumen and of destroying germs. It thus acts as an astringent on all mucous membranes.
The treatment of strychnine poisoning is to immediately evacuate the stomach with a stomach-pump or emetic, chloroform being administered to allay the spasms. If the patient can swallow, draughts of water containing tannic acid may be given.
In these the variety of tannic acid is not exactly the same, but although there are slight chemical differences, they all possess the power of tanning raw hides and of preserving albuminous tissues.
This substance differs from the mucins by being precipitated by tannic acid but not by acetic acid, and being endowed with a higher proportion of sulphur.
The results of applying tannic acid are to harden the pelt and discolour and weaken the fur.
From tannic acid is also made gallic acid, which resembles tannic acid but has no astringent taste.
In the intestine tannic acid controls intestinal bleeding, acting as a powerful astringent and causing constipation; for this reason it has been recommended to check diarrhoea.
For bleeding haemorrhoids tannic acid suppositories are useful, or tannic acid can be dusted on directly.
Since the introduction of iron ships teak has supplanted oak, because it contains an essential oil which preserves iron and steel, instead of corroding them like the tannic acid contained in oak.