PLA>T DERMATITIS 175 



nettle do not protect it from the attacks of swanns of caterpillars : 

 many other so-called " means of defence " seem to be very doubtfully 

 intentional or effective. 



From the point of view of human contact with plants, the irritant 

 materials may be divided into two classes : those substances which 

 are soluble in water (nettle type), and those which are of an oily 

 nature or are soluble in oily secretions (Hhus type). In both cases 

 soap and water, freely applied, is the most natural and effective 

 remedy, and one which is within the reach of all. In addition, it 

 seems likely that ani/ rough hairs or prickles may abrade a delicate 

 skin ; that almost any cell-sap may act as an irritant, and that the 

 combined effect of the two on a susceptible person may produce a 

 case of so-called ** poisoning." This would account for the inclusion 

 in the lists of poisonous plants of such apparently innocuous forms as 

 Doronicum, Helianthiis, Lycoioersicum, Mf/osot is, etc. At the same 

 time it caimot be denied that there are plants which produce results 

 much too serious to be trifled with, and it is advisable to know and 

 avoid them. In dealing with all such plants it cannot be too 

 strongly insisted upon that the most important factor is personal 

 cleanliness. This applies with all the more force to industrial cases 

 in which compensation iiciRy be sought. 



The cases described above have been selected as examples of the 

 commoner and better-known types of Plant Dermatitis, especially those 

 in which there is some experimental evidence of the nature of the 

 actual irritant. A great deal of work remains to be done in that 

 field, in isolating the toxic principles, determining their chemical 

 composition, and examining their actual mode of action on the skin. 

 This-, however, rather leaves the domain of Botany and trenches upon 

 that of Medicine. The poisonous principles are not necessarilv 

 characteristic of all the members of a single genus, and they are 

 so dependent upon external conditions for their development, that 

 the whole subject is of practical rather than of academic interest, 

 since it is unlikely that any valuable clues to classification or evo- 

 lutionary ideas will be obtained from the study of a subject in which 

 individual idiosyncrasy plays such a large part as it does in plant 

 dermatitis. 



The following plants have been known to cause Dermatitis: — 

 Anacardium occidentale (J. C. White, Boston Med. Journ. 1897) ; 

 Arctiitm Lappa:, Angelica (Brit. Journ. Dermatol, xi. p. 287); 

 Asparagus ; Balsam ; Catalpa hignonioides ; CJirysantliemum sp. 

 (Dawson, Brit. Journ. Dermatol. 1906, p. 439) ; Citrus Aurantium 

 \SiV. Bigaradia; Colchicum; Convallaria\ C ot on easier {Cooler, l^rit. 

 Journ. Dermatol, xiii. 1900, p. 183) ; Gucurlita ; Cypripedium Cal- 

 ceolus ; Daphne Mezereum ; Delphinium; Doronicum (Brit. Med. 

 Journ. 1898, vol. i. p. 124-1) ; Eucalyptus hemiphloia (J. Maiden, 

 Lancet, 1904, vol. i. p. 1204) ; Euphorbia ; Ficus ; Helianthus ; 

 Heracleum ; Humea elegans (N. Walker, Introd. to Dermatology) ; 

 Humulus Lupulus ; Laportea gigas ; Narcissus spp. ; Nerium 

 Oleander \ Pastinaca sativa ; Polygonum punctatum (Lloyd, Brit. 

 Med. Journ. 1914, vol. ii. p. 837) ; Primula obcouica, P. mollis, 

 P. si/iensis; Psoralca esculenta ; Bhus Cotinus, B. Toxicodendron. 



