Among diseases which are undoubtedly caused by floating matter in the air
must be reckoned the well-known malady "hay fever," which is a veritable
scourge during the summer months to a certain percentage of persons, who
have, probably, a peculiarly sensitive organization to begin with, and
are, in a scientific sense, "irritable."
This disease has been most thoroughly and laboriously investigated by Mr.
Charles Blackley, of Manchester, who, being himself a martyr to hay
fever, spent ten years in investigating the subject, and published the
result in 1873, in a small work entitled "Experimental Researches on the
Causes and Nature of _Catarrhus aestivus_ (hay fever or hay asthma)."
Mr. Blackley had little difficulty in determining that the cause of his
trouble was the pollen of grasses and flowers, and his investigations
showed that the pollen of some plants was far more irritating than the
pollen of others. The pollen of rye, for example, produced very severe
symptoms of catarrh and asthma, when inhaled by the nose or mouth. Mr.
Blackley came to the conclusion that the action of the pollen was partly
chemical and partly mechanical, and that the full effect was not produced
until the outer envelope burst and allowed of the escape of the granular
contents.
Having satisfied himself that pollen was capable of producing all the
symptoms of hay fever, Mr. Blackley next sought to determine, by a series
of experiments, the quantity of pollen found floating in the atmosphere
during the prevalence of hay fever, and its relation to the intensity of
the symptoms. The amount of pollen was determined by exposing slips of
glass, each having an area of a square centimeter, and coated with a
sticky mixture of glycerine, water, proof spirit, and a little carbolic
acid. Mr. Blackley gives two tables, showing the average number of pollen
grains collected in twenty-four hours on one square of glass, between May
28 and August 21, in both a rural and an urban position. The maximum both
in town and country was reached on June 28, when in the town 105 pollen
grains were deposited, and in the country 880 grains. The number of
grains deposited was found to vary much, falling almost to zero during
heavy rain and rising to a maximum if the rain were followed by bright
sunshine. Mr. Blackley found that the severity of his own symptoms
closely corresponded to the number of pollen grains deposited on his
glasses. Mr. Blackley devised some very ingenious experiments to
determine the number of grains floating in the air at different
altitudes. The experiments were conducted by means of a kite, to which
the slips of glass were attached, fixed in an ingenious apparatus, by
means of which the surface of the glass was kept covered until a
considerable altitude had been reached. Mr. Blackley's first experiment
gave as a result that 104 pollen grains were deposited in the glass
attached to the kite, while only 10 were deposited on a glass near the
ground. This experiment was repeated. Again and again, and always with
the same result, there was more pollen in the upper strata of the air
than in the lower.
A very interesting experiment was performed at Filey, in June, 1870. A
breeze was blowing from the sea, and had been blowing for 12 or 15
hours. Mr. Blackley flew his kite to an elevation of 1,000 feet. The
glass attached to the kite was exposed for three hours, and on it there
were 80 grains of pollen, whereas a similar glass, exposed at the margin
of the water, showed no pollen nor any organic form. Whence came this
pollen collected on the upper glass? Probably from Holland or Denmark.
Possibly from some point nearer the center of Europe.