“But there exists a class of substances no less fatal than the preceding, originating in certain decompositions. In a preceding Chapter (III.) we have inquired into the origin of these poisons, and shown them to originate in fermentation and putrefaction. Let us apply the chemical principles regulating these processes to organic matters, to the products of the animal economy; all the elements of these matters are derived from the blood, the most complex of all existing substances. In decomposing, a poison is occasionally produced speedily mortal when it comes in contact with the blood of the living animal. The venomous principle produced by decomposing animal bodies is not always the same: that originating in certain German sausages is quite peculiar; the person who partakes of this fatal dish dies mummified; he does not rot or fall to pieces like those who perish from wounds received in dissecting-rooms; on the contrary, he dries up and withers, but does not putrify.[50] Liebig, the discoverer of this poison and its effects on man, states that the venom is destroyed by boiling-water and alcohol, but that these do not absorb it. [50] All constitutions are not equally liable to be affected by morbid poisons. This has been proved as regards dissecting-room wounds; and as regards typhus, cholera, plague, ague, &c., the matter admits of no doubt. Similar in the mode of action on the economy are the poisons of small-pox, plague, &c. The substances which arrest fermentation and putrefaction, also neutralize the power of these poisons; but the essence of these poisons has not yet been obtained in an isolated form, and thus nothing positive is known of its real nature. One thing seems certain; contagions, poisons and miasms are not living beings nor animalcules, any more than yeast. They may be, and probably are, produced by fermentation, but this is neither caused by nor terminates in the formation of living animalcules, to which all or any of these phenomena might be attributed. A nice distinction has been drawn by a distinguished chemist between a contagion properly so-called and a miasm. When the disease-producing matter is the product of a disease, it is a contagion; if it be the product of putrefaction or of eremacausis of any substance, animal or vegetable,--does it act by virtue of its chemical character, and not of its condition (_etat_), in forming a combination, or in causing a decomposition, it is then a miasm.