Active Ingredients. - When a branch or leaf of this plant is broken off, there exudes a yellowish milky juice, which in a little while turns black. So poisonous is this juice, that even the atmosphere surrounding the shrub is said to be tainted with emanations from it; the poisonous matter appearing to be volatile, and thus capable of diffusion, even without breakage of the stem or leaf. The researches of Maisch have proved that the cause of the acridity of the juice is the presence of a volatile acid - Toxicodendric acid - which, when isolated, is found to produce effects upon the skin and mucous membranes exactly analogous to those which will be mentioned under the physiological action of rhus.

(According to Cazin, the exhalations of rhus, collected in full daylight, are a nitrogenous gas with a little water, neither of which are irritating; but, on the contrary, the gas collected after sundown is found to be a carburetted hydrogen, mixed with a peculiar acrid principle. The dried leaves do not furnish noxious emanations.)

Physiological Action. - The effects produced by rhus, whether it be taken internally or absorbed by the skin (either from exhalations from the plant, or otherwise), are redness and swelling of the affected parts; and, if referable to exhalations, most particularly in the face and eyes, in which last there is burning, with inflammation of the lids, and agglutination of these organs in the morning. Subsequently there is swelling, with pain, and often a considerable increase of temperature, and the inflamed surface is generally studded with vesicles. Combined with these symptoms, there is an almost unbearable amount of itching, which is not confined to the patches of inflammation, but diffuses itself, more or less, over the entire surface of the body, the hairy portions appearing to be very specially affected. The condition induced thus appears to be of an erythematous or erysipelatous type. It is superficial but spreads rapidly over the surface, and speedily involves large areas of the body; eventually extending to the mucous membranes, as indicated by redness and swelling of the throat and mouth, with, ordinarily, great thirst, irritable cough, nausea, vomiting, vertigo, dulness and stupefaction of head, and colicky pains throughout the abdomen. These last are chiefly experienced during the night, and are aggravated by eating or drinking. Diarrhoea frequently ensues, accompanied by tenesmus, and the stools are often bloody. There is often retention of the urine, or else diuresis, and the water is frequently accompanied by blood.

Rhus also induces pains, apparently of a rheumatic kind, and which are felt not only in the limbs, but in the body, though most especially about the joints. Pain and stiffness in the lumbar regions are often induced, and to these affections is often added a sense of numbness in the lower extremities. The structures most powerfully affected appear to be the fibrous ones. The pains in question are accompanied by a very slight amount of swelling; and, singular to say, they become intensified by rest and warmth. Sleep is greatly disturbed, the patient becoming restless, constantly turning about, and often suffering from great nervous depression.

The fever which sometimes accompanies the effects of rhus, though by no means an universal symptom, usually occurs, when present, in the later stages, and generally partakes of a typhoid character. It is often attended by delirium; the lips are apt to become dry and parched, and to be covered with a brownish crust. Sometimes it assumes an intermittent character, and is then usually marked by profuse perspiration.

The above-described effects of rhus, though so distressing to whoever may have to endure them, appear, however, to be very seldom fatal; and it is remarkable that a certain constitutional predisposition appears requisite to their occurrence, so that it is only individuals who are in danger. Were it otherwise, a plant so common in its native country as the present would be a perpetual source of trouble to the persons dwelling near. I have myself witnessed several instances of its poisonous influence, and can personally vouch for the manifestation of nearly all the phenomena that have been indicated.

Therapeutic Action. - The properties of the Rhus Toxicodendron were first brought into notice about the year 1798, by Dufresnoy, a physician at Valenciennes. Alderson, in England, likewise made some interesting observations with regard to them. Dufresnoy's attention was attracted to the plant by the circumstance of a young man, who had suffered from a six years' eruption upon his wrist, being cured by accidental subjection to its influence; and shortly afterwards he employed it successfully in various cases of obstinate herpetic eruption. Herpes zoster, pemphigus, and eczema, especially when accompanied by burning or itching sensations, represent the class of eruptions which are very readily subdued by the external and internal exhibition of rhus; and in erythema and eryipelas, especially when accompanied by vesicles and bulla?, it is without question a very useful remedy.

(As Dufresnoy was the first to study the plant from a therapeutic stand-point, it may not be out of place to introduce the following anecdote as related in his original work: 1 One day when lecturing on Rhus at the botanical garden of Valenciennes, a mischievous student said to a young florist who was present, that the professor's account of the noxious properties of rhus was incorrect, as the plant growing in France was perfectly innocent. To convince him of this, he plucked some leaves and rubbed them freely on his hands and wrists, as he knew by previous experience he could do with impunity. The florist thus persuaded, followed his example, but in a short time had occasion to repent his imprudence. The next day, finding himself in trouble, he consulted the student, who gravely assured him that he had caught the itch somewhere, and advised him to rub into his hands half an ounce of citrine ointment, and to purge himself freely with mercurial pills. This did not mend matters, and finally Dufresnoy was made acquainted with the state of affairs. In about ten days the young man recovered from the effects of the rhus, and to his great surprise found that a chronic eczema of six years' standing, for which he had vainly sought relief, had disappeared at the same time.