_b. Stomach-Anæsthetics._--There is a class of medicines used in Gastrodynia which seem to act locally on the sentient nerves of the stomach, in the same way that Aconite acts on the superficial nerves of the skin. Although the majority of them are subsequently absorbed, yet, in order to exert this particular action, it is not necessary that they should pass beyond the substance of the stomach itself. They do not seem to have any special or peculiar tendencies towards the stomach nerves. But if introduced into the blood elsewhere, they would not pass the nerves of the stomach in so concentrated a form as when coming directly from the mouth, and thus would not be so useful as stomach-anæsthetics. Thus this action depends upon local contact, and is so far a local action. Hydrocyanic acid, Creosote, and Nitrate (also called Tris-Nitrate) of Bismuth, are the most useful of these medicines. The first two are subsequently absorbed, and pass into the blood. The third is a very insoluble salt. It acts also as an astringent on the mucous surface of the intestine, and is probably the only astringent which is not absorbed. Being insoluble, its action is quite confined to the mucous surface. It may be given safely in very large doses, (as [dram]ss, or even [dram]j.) and it is likely that its anæsthetic action may be in some part mechanical in nature, and depend upon its affording a mechanical sheath to the irritable and painful surface of the stomach. Hydrocyanic acid and Creosote,--general sedatives,--act locally as anodynes to the nerves of the stomach.