37 



to bacteria. Experiments seemed to verify each of these ideas in turn, 

 but that all were erroneous has recently been shown by the discovery 

 that the poison is in reality a nonvolatile oil. In January, 1895, Dr. 

 Franz Pfaff, of the Harvard University Medical School, announced this 

 discovery. The oil has since been purified and named toxicodendrol. 

 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 re- 

 moved by alcohol. Alkalies 

 saponify it and thus render it 

 inert, but the oil is very much 

 more easily destroyed, as 

 Pfaff has shown, by an alco- 

 holic solution of the sugar of 

 lead (lead acetate). 



Effect of the poison. — Numer- 

 ous experiments show con- 

 clusively 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 iu 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 spread- 

 ing. At the end of an hour 

 one of the spots was thor- 

 oughly washed by successive 

 applications of alcohol; in 

 three hours the oil from a sec- 

 ond 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. 



Remedies. — In practice it is not desirable to use strong alcohol, which 



Fig. 19. — Poison sumac (Rhus vemix), showing leaves, 

 fruit, and leaf-scars, one-fourth natural size. 



