Auguste Laurent began his work on morphine, nicotine, and other intoxicating alkaloids hopeful that he could reproduce them artificially from the byproducts of coal tar. After successfully creating artificial alkaloids, he collaborated with Jean-Baptiste Biot to determine that while plant-derived alkaloids were optically active, his artificial ones were not, further establishing a link between the action of molecules upon polarised light and their action upon the animal economy, and a firm line between natural and artificial products later taken up in the work of Louis Pasteur. This paper places this work in the context of a long tradition in which chemists, naturalists, and pharmacists variously used "active principles" to refer both to the particular living nature of substances, and to their ability to act on the human body.