DUST AS A CAUSE OF HAY FEVER. 371 



in fact it probably is freer from dust than the exterior 

 atmosphere near the earth's surface. 



Some remarkable experiments of somewhat analogous 

 nature to that just described were also recently car- 

 ried out in London, in connection with the study of 

 "Hay Fever." The object of them was to ascertain 

 whether the pollen of certain species of grass (notably 

 that of " Anthroxanthum Odoratum," a scented grass 

 that principally gives the delicious aroma to our 

 British hay), and other flowering plants, which are 

 known to cause attacks of this affection, when in- 

 haled by certain persons could be detected in the 

 atmosphere of central London. For this purpose 

 slips of glass, coated with a film of adhesive matter, 

 were exposed to the air during the hay-making season, 

 in various parts of London, and the results of a 

 microscopic examination of the adherent particles proved 

 that even in the heart of London these glasses were 

 generally more or less coated by the pollen of such 

 plants, in considerable abundance. * 



Pollen, we need hardly say, is the powdery substance 

 produced in the stamens of flowering plants, it is one 

 of the commonest of the vegetable substances found 

 in the air, and the amount that is sometimes carried 

 by the wind from place to place, may be judged of 

 from a fact related by the late Mr. Charles Darwin, 

 who states that the ground near St. Louis, in Missouri, 

 has been seen covered with pollen, as if it had been 

 sprinkled with sulphur, and there is good reason, he 



* See Sir Morel Mackenzie on Hay Fever and Paroxysmal Sneezing, 

 4th Edit. 1887, PP- 45 7- (We must, however, remind our readers, 

 that these two affections are distinct diseases of the mucous membrane, 

 and that people suffer from the latter form of it who are in no way 

 affected by hay-making.) 



