57 



usually lasting only a few minutes at a time. A dry scale formed 

 over the surface and remained for several weeks after all irrita- 

 tion ceased. 



In no case did the poisonous action extend beyond the sur- 

 face to which it was applied, thus proving that the action is en- 

 tirely local. If the surface, which has been in contact with the 

 poison, is not thoroughly washed with some solvent like alcohol, 

 benzin, ether or kerosene, the poison will be transmitted to other 

 parts of the body As all kinds of fats and oils are solvents for the 

 poison they should not be used as remedies. Should pustules form, 

 the surface should be frequently washed to prevent the serum from 

 being conveyed to other parts, as it is quite possible that it may 

 be active. Experiments to determine this fact will be conducted 

 in the near future. 



The poison has not at the present time been isolated in a 

 pure condition. 



Dr. Jadassohn and his assistants, Drs, Winckler and Schulz, 

 made 26 tests with parts of the lac obtained under different con- 

 ditions. 



Only that portion which is completely soluble in benzin is 

 poisonous, and this, we have previously seen, was separated 

 by shaking out the benzin solution with alcohol, into two parts, 

 one soluble in alcohol and poisonous, the other insoluble in alco- 

 hol but soluble in benzin and non-poisonous. I have elsewhere 

 stated that by fractional precipitation with lead acetate a partial 

 separation of the poison was obtained, but that I did not consider 

 it a practical method. 



After the above experiments with the poison were made I 

 received from Dr. F. Pfaff a reprint of his article "On the Ac- 

 tive Principle of Rhus Toxicodendron and Rhus Venenata." 90 As 

 the poisonous action of these plants is practically identical with 

 that of Rhus vernicifera, his work is of special interest in this 

 connection. He has conclusively proved that the poisonous prin- 

 ciple of poison ivy is non-volatile, thus> shatter'"^ the false idea 

 that has existed for so many years. He claims to have separated 

 the poisonous principle in a pure form by fractional precipitation 

 with lead acetate as an oil. Dr. Pfaff gives the composition of 

 his lead compound as C 21 H 30 O 4 Pb 6 and proposes the name "Tox- 



10 The Journal of Experimental Medicine, Vol. II, No. 2, p. 181, 

 1897. 



