§ 2. When a chemical substance is applied externally or internally to the living tissues of an animal sufficiently strong to dissolve the affinity between them and the vital force, and to substitute for it other stronger affinities, the explanation of the phenomena is easy, and the coarsest chemistry offers a solution. The action of caustic potass, of concentrated sulphuric acid, present the examples of this kind of dissolution. Other substances alone poisonous when given in concentrated doses, are known to pass, when sufficiently diluted, through the blood, and be eliminated by secretion and excretion from the body: after causing disturbances more or less grave, more or less important, the combinations they form, if any, with the living organic molecules are overcome by the vital force, which then resumes its usual influence. Of such substances some pass off unaltered, others are decomposed, and the bases only appear in the secretions or excretions. Whilst passing through the lungs, certain of these vegetable salts combine with the oxygen of the air, and the respiration in consequence becomes slower, or in other terms, they diminish the production of arterial blood.[47] [47] I am free to admit, with Liebig, that the lungs are the seat of the most rapid and powerful chemical action (p. 151), yet some distinguished physiologists think that the external integuments may become the seat of disease, and give origin to dangerous affections by mere stoppage of their secretions and excretions. Certain of these are held to be poisonous and highly irritating, and cholera itself has been ascribed to the sudden transfer of the tegumentary secretions into the general torrent of the blood. This seems to have been the opinion of the celebrated anatomist and physiologist, De Blainville. Now, these salts[48] when placed in contact with animal and vegetable substances, perform the same function as in the lungs: they take a part in the combustion going on, and, as in the living body, are converted into carbonates. Left to themselves for a time, from their aqueous solution, the acids composing them finally completely disappear. [48] Citrates, tartrates, acetates. Mineral acids and nonvolatile vegetable acids, as well as mineral salts with an alkaline base, have the property, when sufficiently concentrated, to arrest the whole process of this slow combustion;[49] common salt, as is well-known, arrests putrefaction: so does alcohol. [49] Eremacaasie: Liebig. The chemical action of certain other mineral salts is different, such as the salts of the peroxide of iron, of lead, bismuth, copper, and mercury. These are inorganic poisons. They combine with the tissues of the organs, and so destroy life. The mode of action of the poisons of prussic acid, strychnine, morphine, &c., is as yet unknown.