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AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
Millon (35), evidently unaware of the work of Khittel, also investigated 
R. Toxicodendron. He believed the poison a non- volatile gum resin re- 
quiring direct contact to cause dermatitis. He found its alcoholic solution 
to be toxic. 
Discussing the experiments of Khittel, Maisch (33) held the poison to 
be volatile and said : 
It is natural to suppose that, during the process of drying, the greatest portion of the 
poisonous principle should be lost. This must be still greater, if the dried leaves are 
powdered, a hot infusion prepared from them, and this infusion evaporated down to the 
original weight of the dried leaves. It is obvious that Khittel could not have selected a 
better method for obtaining the least possible quantity of the poisonous principle, if, indeed, 
it could be obtained by this process at all. 
Later Maisch (34) disagreed with Khittel and denied the presence of a 
volatile alkaloid. He thought that he had found a new volatile acid, which 
he held to be the active principle and which he called " toxicodendric acid." 
Maisch enclosed in a tin box a lot of freshly collected leaves of poison ivy, 
and introduced into this box a number of moistened test papers. The 
next morning he found that the blue litmus paper had been colored strongly 
red, w^hereas curcuma and red litmus paper were unaffected. He writes 
regarding this experiment: 
This single experiment was at once a conclusive proof that the exhalations of these 
leaves contained a volatile acid, and that the poisonous properties were most likely due to it. 
Maisch describes further how he obtained an impure watery solution of 
his toxicodendric acid by maceration of the leaves, expression and distil- 
lation of the expressed liquid. In preparing his acid, he suffered from a 
copious eruption and the formation of numerous vesicles on the back of his 
hands, fingers, wrists, and bare arms. He says further: 
Several persons coming into the room while I was engaged with it were more or less 
poisoned by the vapours diffused in the room, and I even transferred the poisonous effects 
to some other persons merely by shaking hands with them. The dilute acid, as obtained 
by me, and stronger solutions of its salts, were applied to several persons, and eruptions 
were produced in several instances, probably by the former, though not always, which was 
not likely owing to the dilute state of the acid. 
Maisch did not isolate his acid nor any one of its salts; he never had the 
substance in question chemically pure. He proved only the presence of a 
volatile acid. He noticed the characteristic eruption on his own skin 
while working with the poison ivy. Persons coming to the laboratory at 
this time were often poisoned. He observed also that an eruption some- 
times followed the application of the impure solution of this acid to the skin. 
From these very rudimentary experiments he drew the wholly unwarranted 
conclusion that his acid must be the active principle. 
By far the most valuable work on Rhus Toxicodendron is that of Pfafif 
(37). From a clinical study of Rhus poisoning, Pfaff came to the conclusion 
that the poison must be a non-volatile skin irritant. The more volatile 
