Carrot poultices are still more useful, as they possess the property of abating the fœtor, in a degree superior to the hemlock, and give generally as much ease. This fœtor has been long compared to the smell of hepar sulphuris, and lately has been supposed to arise altogether from the formation of a substance of this nature, consisting of sulphur and volatile alkali. As it has been too much the case in medicine, to overlook causes, and attend to effects, so we are not to be surprised, if we find some physicians proposing to cure cancer, by remedies which shall decompose the matter which is yielded in that disease, or destroy the effect of the morbid action, whilst the action itself is overlooked[144]. From experiments made upon the hepatized ammonia, it was found, that the oxygenated muriatic acid was the best agent for decomposing it, and destroying its smell. This fluid was, therefore, highly recommended as an application for cancerous sores; and, in many instances, it will indeed be found to correct the fœtor, which is certainly one advantage; but it never will perform a cure. [144] Although the fœtor may depend upon the presence of hepatized ammonia, yet this does no harm to the ulcer. On the contrary, I have sometimes found the application of this fluid, when mixed with water, have the effect of abating the pain. Carbonic acid has been said not only to correct the fœtor, but also, in some instances, completely to cure the disease. It was long ago proposed by M. Peyrilhe, and of late it has again been brought forward by Dr. Ewart, who has published a case in which it produced cicatrization; but although, upon his recommendation, it has been frequently employed, yet it has very seldom been of any considerable service, and I have heard of no instance in which it produced any permanent amendment. It would rather appear, that the opinion of M. de Fourcroy was the just one: “After the first applications (says he), the cancerous sore appears to assume a more favourable aspect, the sanies which flowed from it becomes whiter, thicker, and purer, and the flesh has a redder and fresher colour; but these flattering appearances are deceitful, nor do they continue long, for the sore speedily returns to its former state, and its progress goes on as before the application.” The best method of applying this, is by means of a bladder, the mouth of which is fastened round the sore, by means of adhesive plaster. The air is introduced by a pipe inserted at the other end. When first applied, the gas produces a sensation of coldness, which is soon followed by a glowing heat, and abatement of the peculiar pain of the sore. At other times, it, from the first, produces a smarting, and makes the patient rather more uneasy. This is especially the case if we use the fermenting poultice, instead of the air already extricated.