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DERMATITIS VENENATA 



I. THE RHUS GROUP. 



This group includes all those plants in which the poisonous 

 principle is contained in a clear, watery juice. 



The ivy or sumac belongs to the genus Rhus Linnaeus, which is 

 classified either as a genus belonging to the superfamily Anacardio- 

 ideae in the family Terebinthaceae, or more simply as belonging to 

 the family Anacardiacese. The genus Rhus includes about 120 

 species, growing in nearly every part of the world ; but fortunately 

 only a few are poisonous to man, and they may be distinguished, 

 as a rule, by their inconspicuous flowers being in loose, slender 

 clusters or panicles in the axils of the leaves, and by their greyish- 

 white or yellowish dry fruit. 



They may be arranged in two sections, according to the structure 

 of their leaves : — 



1. Leaves trifoliate. 



Rhus radicans Linnaeus. 

 Rhus toxicodendron 'Linnxus. 

 Rhus diver siloba Torrey and Gray. 



2. Leaves pinnate. 



Rhus vernix Linnaeus. 

 Rhus pumila Meerburg. 

 Rhus vernicifera De Candolle. 

 Rhus succedanea Linnaeus. . 



Rhus radicans Linnaeus is by many authorities considered to be 

 merely a variety of R. toxicodendron. It is common in the Northern 

 United States, while the latter is more common in the Southern 

 United States. It has ovate or lozenge-shaped leaflets, which are 

 either entire or toothed and pointed, while R. toxicodendron has 

 obtusely crenated, lobed leaves. . 



' Rhus diversiloha is the Californian poison ivy or poison oak, 

 with rounded, obtuse leaflets. 



Rhus vernix (synonym, R. venenata) is the poison elder or poison 

 sumac of the United States, and is a large shrub or small tree. 

 It is very poisonous. 



Rhus pumila Meerburg is a small erect shrub, found in the 

 Southern United States. 



Rhus succedanea Linnaeus is the Japanese wau-tree, and is well 

 known in Tonkin and in South China. 



etiology.— The poisonous principle is an oil (Toxicodendrol) , 

 which occurs in all parts of the plant and at all seasons, and not 

 toxicodendric acid, which is merely a synonym of acetic acid, as 

 was formerly thought to be the case. 



Symptomatology. — After an incubation of one to nine days, 

 there is at first itching in the affected area, which gradually increases 

 in intensity, and is associated with all the signs of inflammation, 

 producing an appearance not unlike erysipelas, arid sometimes 

 going on to vesiculation. The parts most Commoilly affected are 



