There is almost no part of a plant that, in some species at least, has not been found to contain the various acids, alkaloids, oils, essences, and so forth, which make up the chief medicinal or, as the pharmacists call it, the active principle of plants. In certain of them the most violent poisons are produced, such as the poison hemlock which killed Socrates, and the deadly nightshade. And again the unripe pod of one plant produces a milky juice so dangerous that traffic in it is forbidden in all civilized countries, and yet later the seeds from that matured pod are sold by the thousands of pounds to be harmlessly sprinkled on cakes and buns by the confectioners. Earlier in this book it was said that plants are chemical laboratories, and nowhere has this alchemy been carried to such a pitch of perfection as in the hundreds of drugs produced by different plants. Reference to special books on that subject should be made by those interested, as only a few of our most important drug plants can be mentioned here. QUININE The Spanish viceroy of Peru, whose wife, the Countess del Chinchón, was dangerously ill of a fever in that country about 1638, succeeded through the aid of some Jesuit priests in curing the malady, with a medicine which these priests had gotten from the natives. It was a decoction from the bark of a tree, and its fame soon spread throughout the world as Peruvian bark. Even in those days malaria was the curse of the white man in tropical regions, and since then it is hardly too much to say that the discovery of this drug has made possible for white colonists the retention of thousands of square miles of tropical country that without it would in all probability be unfit for occupancy. To the natives, too, quinine has been one of the greatest blessings, and in some of the remote regions of the tropics the writer has found quinine more useful than dollars in getting help from fever-ridden natives, too poor and too remote from civilization to get the drug. For more than a hundred and fifty years after the discovery of Peruvian bark it was always taken as a liquid, usually mixed with port, and an extremely noxious and bitter drink it made. The fine white powder which we now use in tasteless pellets or pills has made the drug even more useful than before.