Abstract
Dunbar was the first to demonstrate conclusively that the European or spring variety of hay fever is caused by the pollen of timothy and other members of the graminaceæ family. He found, that, even in midwinter an aqueous extract of timothy pollen produced flushing and intense irritation when introduced into the eye of a susceptible individual, whilst normal individuals were entirely unaffected by such a procedure.
Sufferers from the American or autumnal form of hay fever (caused by the pollen of ragweed, golden rod, and other members of the Compositæ family) exhibit a similar sensitiveness when tested with aqueous extracts of ragweed pollen. This reaction is also strictly specific, and only those who suffer from both spring and autumnal hay fever react to the extracts obtained from both varieties of pollen. The amount of pollen extract required to produce flushing in the eyes of sensitive individuals varies from 1/20 of a c.c. of a solution of one in five hundred thousand to 1/20 of a c.c. of a solution of one in five hundred. This test can be utilized quantitatively and affords a fair index of the measure of immunity or resistance possessed by sensitized individuals.
A specific cutaneous reaction capable of quantitative application may be obtained by making a slight abrasion of the skin and applying a drop of pollen extract of suitable concentration. A large white welt similar to that resulting from a mosquito or bee bite accompanied by a distinct itching sensation develops on susceptible individuals within 15 minutes, while normal controls are unaffected. A small dose of pollen extract (1 c.c. of a one in a million for example) injected subcutaneously produces in highly sensitized individuals an itching or prickly sensation followed immediately by considerable swelling at the point of injection and redness extending sometimes over an area of several inches.
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