PL INT DEUMATITIS 133 



acid in a pure condition and found it to be merely acetic acid. Bv 

 distilling- the crushed leaves antl stem in a current of steam, there 

 was obtained, in addition to this acid, small quantities of an oily- 

 substance, which proved to be an active irritant. This oil was 

 obtained in larger quantities hy extracting with alcohol and then 

 distilling oft' the s])irit, leaving a black oily residue which was washed 

 with water and taken up in ether. The etherial solution on washing 

 with water and then dilute solution of sodium carbonate, yielded an 

 impure sample of the oil, which was contaminated by resinous 

 oxidation products. The oil was prepared pure by treating with 10-15 

 times its bulk of 95 "/o alcohol. After standing, fractional precipi- 

 tation with lead acetate gave a precipitate from which the free active 

 oil could be obtained by treating with ammonium sulphide, 'j'he 

 free oil, which Pfaff named " Toxicodendrol," was not analyzed, 

 though the pure lead salt gaye a provisional formula of C^^H^^O^Pb. 

 This oil occurs in all parts of the plant : stems, leaves, fruit, and even 

 on the pollen. It is non-volatile, and the least trace of it is irritant : 

 e. g. in one case '005 mg. in two drops of olive oil caused severe pain 

 and swelling. Experiments with the puritied free oil j^roduced results 

 exactly similar to a severe case of i^Z/i/s-dermatitis. 'J'hat is to say, 

 the attack was characterized by swelling, localized redness, and the 

 formation of papules which developed in the course of a few days 

 into vesicles (which became confluent in many cases), with consider- 

 able exudation of serous fluid and the formation of crusts. The 

 attack lasted about 15 days, and at its height the pain and fever 

 were considerable. The poison being a very sticky, non-volatile oil, 

 apparently excreted by the epidermal cells of actively j^hotosynthetic 

 leaves during the warm season (the plant is considerably more 

 virulent in America than in this country, and the leaves are not 

 poisonous in autumn, i. e. when photosynthesis is not active owing to 

 cold, etc.), which is slowly oxidized in contact with air to a resin, the 

 usual methods of treatment by bland ointments such as carbolized 

 vaseline, by lotions, etc., are only too well calculated to spread the 

 trouble instead of checking it. These substances, such as mutton fat 

 or petroleum jelly, become almost liquid at body temperature, and so 

 dissolve the oil and carry it to other parts of the body. This was 

 clearly demonstrated in the case described above ; the fingers of the 

 unaffected hand, which came in contact with the other while dressing 

 it, became poisoned, and so did the arm wherever the dressing had 

 reached. On the other hand, immediate relief was experienced when 

 the injured arm was scrubbed with soap and water, and the swelling, 

 etc. rapidly subsided under this treatment. Dr. Pfaff found that in 

 all cases the best treatment was vigorous mechanical removal of the 

 poisonous oil by scrubbing with soap and water, with or without a 

 preliminary treatment with alcohol. This method answered at any 

 stage of the attack. One point about this dermatitis which makes it 

 rather difficult to diagnose is the fact that there is a " latent period " 

 after contact with the plant before the attack begins. This time 

 varies from 18-24 hours, to as long as 7-9 days, the average time 

 being four or five days, by which time most people would have 

 forgotten an accidental contact with the plant. This "latent time" 

 probably indicates the time taken for the oil to infiltrate the skin, 



