182 TTIK .TOUIIXAL OF BOTxVN^Y 



and even other parts of the body. The itchhig and fever may be 

 intolerable, completely preventing sleep, and rapidly wearing out the 

 patient by loss of rest and lack of appetite. There may be only a 

 single attack, or they may be recurrent at short intervals over several 

 months of the year, and tinally settle down into a chronic condition 

 which is extremely distressing. The great regularity with which 

 such cases respond favourably to change of scene, but as regularly 

 relapse on returning home (to the source of irritation), might lead to 

 a suspicion of their environmental origin, but frequently mvich time 

 and trouble are wasted owing to ignorance on the part of both patient 

 and physician. Of course, as soon as the offending plant is discovered 

 and destroyed, recovery is rapid and complete, unless the case has 

 become chronic. The irritant in this case is an oil, which is secreted 

 by glandular hairs all over the leaves and stalk. External conditions 

 are known to have a marked effect upon the development of the oil, 

 so that a person who has hitherto been immune, may, on coming into 

 contact with plants in another locality, be badly poisoned [Weydahl, 

 1908]. The hairs are normal glandular trichomes, and usually con- 

 sist of three cells : two more or less elongated as a stalk, and one 

 smaller, rounded head-cell with dense contents. The oily substance 

 is secreted in the usual way beneath the cuticle of the head-cell, so 

 that the former is gradually distended until it bursts, and the secretion 

 is poured out and trickles down the hair. (For stages in the develop- 

 ment of the secretion in Primula ohconica, P. sinensis, and 

 P. mollis, cf. Nestler, 1904 and 1908). The hairs are very delicate 

 and easily broken, consequently the skin is readily affected by the 

 oily substance, and in the case of susceptible individuals the usual 

 impleasant symptoms follow. It is extremely eas^^ to transfer the 

 irritant to other parts of the body, and every place touched will be 

 att'ected in a greater or less degree, according to the thickness of the 

 cuticle at the spot. 



III. A similar but even more serious type is the poisoning 

 produced by species of Pints, such as Phus Toxicodendron ("Poison 

 Ivy"), P. venenata (-'Poison Elder"), and other forms such as 

 P. Cotinus, P. Coriaria, P. vernicifera. (The last is the plant 

 from which Japanese lacquer is obtained, and will be dealt with 

 later.) -Phus Toxicodendron was put on the market in recent years 

 as an ornamental plant under the trade-name of '* Ampelopsis 

 Hoggii,"'' owing to a general resemblance to the North American 

 Ampelopsis quinqvefolia, Virginian Creeper, of commerce, from which 

 it can be distinguished at once by having three instead of five leaflets 

 in its compound leaf. Masquemding under this name, the plant was 

 employed as a decorative climber by many unfortunate people, some 

 of whom suffered severely for their ignorance. A case is known 

 where the plant grew up and surrounded a bedroom window : the 

 owner of the house and his wife, who occupied the room, were both 

 poisoned on the face while handling the foliage when opening or 

 shutting the window, with very serious results. 



The active principle of Phus Toxicodendron and P. venenata was 

 investigated by Pfaff. An older view ascribed the toxic qualities to 

 an acid which w^as extracted from the plant, just as the stings of 

 nettles were supposed to be due to formic acid. Pfaff prepared this 



