36 The Ottawa Naturalist. [May 



off within about an hour of its first contact, no ill results ensue, 

 unless, perhaps, if one is very susceptible; and. as is well known, 

 individuals differ vastly as regards susceptibility. . Some people 

 contract the disease in a more or less severe form regularlv everv 

 summer; others appear to be quite unaffected. And, after all, 

 the large majority are practically immune. For, when one con- 

 siders the wide distribution and great profusion of the plant, it is 

 evident that only a comparatively small percentage of those 

 who come within its evil sphere of influence are poisoned by it. 

 At the same time it is very doubtful to my mind if any one is 

 perfectly immune. Given certain favorable, or rather unfavor- 

 able conditions, particularly heat and moisture, and no one is 

 safe from the attack. A friend of mine, a lumberman, who has 

 spent all his life in the woods, and must have been continuallv 

 exposed to the infection ever since his boyhood. was a few years ago 

 badly poisoned for the first and only time in his life. One damp 

 warm day in June he had occasion to walk some distance through 

 a bush infested with poison ivy just when the latter was in bloom. 

 In slapping at the mosquitoes, which were very troublesome, he 

 doubtless transferred the acrid oil from the leaves or pollen to 

 his face. For a day or two after he suffered a very severe attack 

 which completely closed up his eyes. I was myself for years 

 under the impression that I was quite immune, and often handled 

 the plant with impunity, until one day I inadvertently dropped 

 my cap into a clump that was in blossom. The pollen evidently 

 shook eff into the cap and thus came into contact with my skin. 

 for a day or two later the familiar vesicular sore broke out across 

 my forehead. Annual recurrences of attacks without any fresh 

 exposure to the infection are occasionally reported. Some of 

 these may safely be referred to traces of oil remaining on summer 

 clothing that is resumed the next year; but. there are others 

 that are not so easily accounted for. I have been told of an 

 attack first contracted by stepping on the plant with a wet and 

 naked foot, which recurred regularly, without new infection, 

 everv vear for seven years. That mystic number "seven" 

 might cast a shade of suspicion, if I had not the fullest confidence 

 in the accuracy of my informant, who is an expert botanist and a 

 scientific observer, and who had personal knowledge of the occur- 

 ence. If, as seemed to be shown by some of Mr. Chestnut's 

 experiments mentioned above, the irritation is purely local ai 

 external, it is exceedingly difficult to account for such attacks, 

 and the only explanation I can offer, and I hat very tentatively 

 is that they are the result of autosuggestion. But here wo plun 

 into physiological psychology, and if 1 wan to keep within my 

 depth I had better stop. 



Alleged remedies are numerous. Most of them owe their 



