
June 16, 1923] 
NATURE 
813 

conjunctiva, or by inhalation or actual inoculation in’ 
the skin—the most approved modern method of 
diagnosis. Pollen from a number of grasses produced 
typical hay fever. Blackley particularly blamed the 
pollen of italian rye-grass (Lolium italicum), meadow 
fox-tail grass (Alopecurus pratensis), rye (Secale cereale), 
wheat (Triticum), oats (Avena sativa), and the common 
hazel-nut (Corylus avellana). He also studied the size 
and shape of different pollen grains, and concluded that 
the disturbance in predisposed persons was due partly 
to the mechanical and partly to the physiological 
action. In experiments on himself, dazzling light and 
heat were ineffective. 
To study the distribution of pollen in the atmo- 
sphere Blackley then undertook a long series of experi- 
ments with ingenious apparatus which he devised, and 
he traced by microscopic methods of enumeration the 
pollen grains in the air in a variety of weather con- 
ditions. From May to the end of July he traced from 
day to day the pollen incidence in the air, and showed 
how it was subject to great fluctuations depending on 
temperature and moisture. About 95 per cent. of 
the pollen found was identified as belonging to the 
Graminaceae. In dwelling-rooms little or no pollen 
was found. By means of moistened glass slips attached 
to the tails of kites flown as high as 1500 feet, Blackley 
made numerous observations both on the sea-shore and 
inland, and demonstrated the remarkable fact that in 
the upper strata of the air there was nineteen times as 
much pollen as was found near the surface of the earth, 
and he showed how pollen can be carried to great 
distances by wind currents in the upper reaches of 
the air. 
Blackley was so far ahead of his time, that despite 
the excellence of his work the causation of hay fever 
was still regarded asa terra incognita. A common idea 
prevailed that it was a nervous disease in certain persons 
with a labile or hysterical nervous organisation. The 
Teinvestigation, on the scientific lines laid down by 
Blackley, led, in the hands of Dunbar (1903), to a 
complete confirmation of his results ; but Dunbar went 
further by proving that the deleterious agent in pollen 
is only its protein. Collecting pollen in large quantities, 
he showed that extracts are highly toxic in hay-fever 
subjects. 
One of Dunbar’s collaborators—Liefmann (1904)— 
found that, at the time of the worst hay-fever 
attacks in the centre of the city of Hamburg, no 
less than 250 grass pollen grains settled in 24 hours 
on a surface measuring 1 square centimetre (z.e. about 
2,500,000 per square metre). Year by year it was 
noted that on the first appearance of pollen in the air 
patients began to suffer from hay fever. In the 
beginning of June grass pollen is in excess of all others, 
and from the third week of July begins to disappear. 
Kammann estimated that 4o per cent. of the pollen 
mass was protein, and a solution of a strength of 
I : 30,000—1 : 1,000,000 dropped into the eye could 
determine an immediate attack of hay fever. Dunbar 
tested the activity of a large number of pollens other 
than those from grasses, but mostly with negative results. 
Besides the pollens of grasses and sedges the following 
pollens were, however, found to be active: honeysuckle 
(Lonicera caprifolium), lily of the valley (Convallaria 
majalis), Solomon’s seal (Polygonatum multiflorum), 
NO. 2798, VOL. 111] 
evening primrose (Ginothera biennis), rape (Brassica 
napus), spinach (Spinacea oleracea), as well as a number 
of Composite and privet (Ligustrum vulgare). These 
experiments were all made in Europe. In the United 
States of America there is a common form of “ hay 
fever” caused not by grass pollen but by pollen 
of golden rod (Solidago), and particularly ragweed 
(Ambrosia elatior). From its occurrence in September 
this variety is widely known as ‘“‘ autumnal ” or “ fall” 
fever. According to the records of the American Hay 
Fever Prevention Association, something like 1 per 
cent. of the whole population (about 1,000,000 cases) 
are liable to June or autumn fever. 
Hay-fever research is being very actively carried 
out in the States, and already a very large number of 
pollens are known to be toxic. Several general prin- 
ciples are emerging from this work; for example, the 
negligible importance of insect-borne pollens as con- 
trasted with the importance of those that are air- 
borne, and the great variations which occur from the 
diversity of the local flora. Important hay-fever and 
botanical surveys are now being compiled from many 
of the American States. The diagnosis of the capacity 
of pollen to produce hay fever is made by cutaneous 
inoculation, by a scratch on the forearm, of a dilution 
of the pollen protein, which may be extracted in several 
different ways. A wheal, 5 or more mm. in diameter, 
surrounded by a red halo and appearing within half 
an hour, is regarded as a positive reaction. 
It is now known that far more plants can produce 
hay fever than was formerly supposed. Indeed the 
term ‘“‘ hay fever’ is quite inappropriate. “‘ Toxic 
pollen idiopathy” has been suggested in its place. Later 
studies have also directed attention to what are called . 
‘“‘sroup reactions.” Thus patients with June fever 
react to grass pollens, while those with autumnal fever 
react mainly to the pollen of composite, such as golden 
rod, golden glow, sunflower, and ragweed. The group 
reaction indicates that the pollens of allied families of 
plants have a common protein chemical constitution. 
Although many different pollens can produce symptoms, 
it does not follow that all such pollens are of practical 
importance in the disease. The principle that only 
anemophilous pollen is the natural toxic agent is very 
important, and thus the entomophilous pollens of 
golden rod, golden glow, sunflower, and daisy, although 
they can produce hay fever, do not do so in practice 
except in unusual circumstances. That such circum- 
stances do occasionally operate is made clear by the 
recent researches of Pott at Bloemfontein. In this 
city he has clearly shown that a severe form of 
pollinosis occurs from October to January, and it is 
caused by the pollen of the pepper tree (Schinus molle). 
Normally this pollen is sticky and is insect-borne, but 
in the hot, dry weather prevailing in Bloemfontein it 
becomes dried and is dispersed by wind. In fact, it 
was the principal and occasionally almost the sole 
pollen deposited on glass plates exposed to the air, 
and it was also demonstrated in the nasal mucous 
secretions of susceptible subjects. Of great importance 
also is the determination of the actual dates of flowering 
of hay-fever plants in each particular district. More 
than 200 plants are known to be capable of setting 
up symptoms of “‘ hay fever.” 
With regard to the nature of the predisposition which 
