I have looked into this matter with care, and I find that (presumably in ignorance) nurserymen in England have sold specimens of the poison-vine for planting as creepers, under the name _Ampelopsis Hoggii_. The smaller-leaved Virginian creeper, with self-attaching tendrils, is known as _Ampelopsis Veitchii_, and is, like the larger Virginian creeper (_A. quinquefoliata_), quite harmless. The poison-vine is not an Ampelopsis at all, not even one of the Vitaceæ or vine family, as that genus is. It is a Sumach or Rhus, and belongs to a distinct family, the Terebinthaceæ. It has a three-split leaf, not five leaflets, as has the large Virginian creeper, nor a small three-pointed leaf, as has the _Ampelopsis Veitchii_. The _Veitchii_ frequently has the leaf also split into three leaflets, but the stalk of the middle leaflet is not relatively so long as it is in the poison-vine. The differences and resemblances in the leaves of these plants are shown in the accompanying illustration (Fig. 14), which has been prepared from actual specimens for this book. The people of the United States are on their guard against this plant, knowing its terrible properties. Sir William Thiselton Dyer, formerly director of Kew Gardens, tells me that specimens of the “American poison-vine” are grown in the garden at Kew, and that he has been present when American visitors (ladies) literally screamed with horror on seeing it, and ran from it as from a mad dog. Several cases are on record of the mysterious poisoning produced by this plant in England; but it is strangely unfamiliar to medical practitioners—indeed, practically unknown to them, although I have ascertained that many English people, especially ladies, have been victims for some years to its unsuspected influence. At the University of Harvard, in Cambridge, Massachusetts, they have made quite recently a thorough examination of the poison-vine in the laboratory, with the following results: The poison is an oil—a fixed oil, not a volatile one, as we might have imagined from its mysterious action at a distance. The oil exists in all parts of the plant, even in the fine hairs and cuticle of the leaf. It can be extracted by means of ether, and is one of the most virulent irritants known, having a very curious penetrating and persistent action, and producing violent pain and destruction of tissue when placed on the skin in quantity so minute (one-thousandth of a milligram in two drops of olive oil) as to be beyond the terms of everyday language. It seems to be usually brought to the eyes, nose, lips, and skin of the face and body by the fingers which have touched a leaf or fragments of a leaf in powder. The dead leaf in winter still retains the oil, and minute dust-like particles can carry it. The treatment for it is washing with soap, oil, and ether at an early stage of the attack—especial care being taken to free the fingers from any minute traces of the oil adhering to them.