VARIOUS FARM PRODUCTS 573 



of the box elder. They differ from those of the Virginia creeper in 

 having only three leaflets instead of five. Poison ivy grows every- 

 where in open brush, in ravines, and on the borders of woods, and it 

 is spread along roadsides and cultivated fields from seeds carried 

 by crows, woodpeckers, and other birds that feed upon its fruit in 

 winter. Through ignorance or carelessness, and at the imminent 

 risk of causing greatly bodily discomfort to many persons, this vine 

 is sometimes planted about suburban and even city residence for the 

 sake of ornament. It occurs wild in abundance throughout the 

 United States as far west as eastern Texas, eastern Kansas, and 

 Minnesota, and in greater or less abundance throughout the less 

 arid region of the west, with the exception of California and the 

 western parts of Oregon and Washington, where it appears to be 

 entirely replaced by Rhus diversiloba. Recent experiments made 

 by Dr. Franz Pfaff, of the Harvard University Medical School, have 

 shown that the poison is a nonvolatile oil. It is found in all parts 

 of the plant, even in the wood after long drying. Like all oils, it 

 is insoluble in water, and can not therefore be washed off the skin 

 with water alone. It is readily removed by alcohol, and very easily 

 destroyed by an alcoholic solution of sugar of lead (lead acetate) . 



Numerous experiments show conclusively that the oil produces 

 precisely the same effect as does the plant itself. When a very 

 minute amount is placed upon the skin, it is gradually absorbed in 

 the course of a day or so, and within certain limits the effect is 

 proportional to the time of contact. In an experiment performed 

 by the writer, the oil was applied to four places on the left wrist, 

 and these were carefully guarded to prevent spreading. At the end 

 of an hour one of the spots was thoroughly washed by successive 

 applications of alcohol; in three hours the oil from a second was 

 washed off in the same manner, and the others were cleansed three 

 hours later. There was little or no effect on the first; that on the 

 second was more marked, but did not equal that produced on the 

 last two, which was about the same in each. The spots were within 

 an inch of each other, but remained wholly distinct, a fact which 

 very clearly shows that the affection is not spread by the blood. 

 Subsequent applications of an alcoholic solution of sugar of lead 

 gave speedy and permanent relief. In practice it is not desirable to 

 use strong alcohol, which is apt to be too irritating to a sensitive sur- 

 face, but a weaker grade of from 50 to 75 per cent is recommended. 

 To this the powdered sugar of lead is to be added until no more will 

 easily dissolve. The milky fluid should then be well rubbed into 

 the affected skin, and the operation repeated several times during 

 the course of a few days. The itching is at once relieved and the 

 further spread of the eruption is checked. 



Poison Oak (Rhus diversiloba}. Poison ivy; yeara; Cali- 

 fornia poison sumac. The poison oak differs from the preceding 

 species mainly in the character of its leaflets, which are somewhat 

 thicker and smaller, more nearly elliptical, and less sharply lobed. 

 Their similarity to the leaves of the Western oaks gives the plant 

 its common name. The poison oak grows at low elevations in open 



