A physician[19] who had a very painful APTHOUS ULCER at the point of his tongue, found great relief, when other remedies failed, from the application of fixed air to the part affected. He held his tongue over an effervescing mixture of potash and vinegar; and as the pain was always mitigated, and generally removed by this vaporisation, he repeated it, whenever the anguish arising from the ulcer was more than usually severe. He tried a combination of potash and oil of vitriol well diluted with water; but this proved stimulant and increased his pain; probably owing to some particles of the acid thrown upon the tongue, by the violence of the effervescence. For a paper stained with the purple juice of radishes, when held at an equal distance over two vessels, the one containing potash and vinegar, the other the same alkali and _Spiritus vitrioli tenuis_, was unchanged by the former, but was spotted with red, in various parts, by the latter. In MALIGNANT FEVERS wines abounding with fixed air may be administered, to check the septic ferment, and sweeten the putrid _colluvies_ in the _primae viae_. If the laxative quality of such liquors be thought an objection to the use of them, wines of a greater age may be given, impregnated with mephitic air, by a simple but ingenious contrivance of my friend Dr. Priestley.[20] The patient's common drink might also be medicated in the same way. A putrid DIARRH[OE]A frequently occurs in the latter stage of such disorder, and it is a most alarming and dangerous symptom. If the discharge be stopped by astringents, a putrid _fomes_ is retained in the body, which aggravates the delirium and increases the fever. On the contrary, if it be suffered to take its course, the strength of the patient must soon be exhausted, and death unavoidably ensue. The injection of mephitic air into the intestines, under these circumstances, bids fair to be highly serviceable. And a case of this deplorable kind, has lately been communicated to me, in which the vapour of chalk and oil of vitriol conveyed into the body by the machine employed for tobacco clysters, quickly restrained the _diarrhoea_, corrected the heat and foetor of the stools, and in two days removed every symptom of danger[21]. Two similar instances of the salutary effects of mephitic air, thus administered, have occurred also in my own practice, the history of which I shall briefly lay before the reader. May we not presume that the same remedy would be equally useful in the DYSENTERY? The experiment is at least worthy of trial.