By the 1880s physicians were leaning in the right direction as to what "causes" an attack of hay fever (about what are the exciting causes). There was still some speculation, although for the most part empirical and scientific evidence was used. Dr. Charles Blackley was among those who frowned upon speculation, and when experiments didn't satiate his desire to know, he left the answer open ended.
Of all the things believed to cause hay fever in 1850s through the 1870s, Dr. Blackley put them all to the test, mainly by experimenting on himself. The following are the common agents he tested: (1)
1. Benzoic acid: What is it? Its salts are used as a food preservative. Blackley spent two hours at a time on three separate occasions and found that no hay fever symptoms resulted.
2. Coumarin: A chemical compound found naturally in some plants, and can be used as a food additive or in some perfumes. He and other men spent a couple hours in a room with a strong odour of the stuff, and this did not result in any hay fever symptoms. The experiment was repeated multiple times with the same resuls.
3. Odours: He inhaled the odours of various plants, flowers, fungi and other substances that produce smells. Some produced symptoms and some didn't. The substance that came closest to producing hay fever symptoms was Penicillium. He therefore recommends further testing in this area.
4. Ozone: It was discovered in 1785 by Dutch physicist Martinus Van Marum (1750-1837). It's a naturally occurring substance created by the sun, although Christian Friedrich Schonbein described in 1832 how it can be produced by man. Dr. Schonbein said he observed catarrhal affections such as asthma and hay fever among those who inhaled air highly charged with it. In 1862, Dr. Phillip Phoebus re-established this observation. Blackley set out to prove if this was true. He spent six hours in his office inhaling the substance and observed no effect. (2, page 35) (8, page 8, pages 79-91) (2, page 35)
5. Dust: Dr. George Beard suggested dust sometimes caused hay fever, and of 198 cases, 104 said dust caused their symptoms of hay fever, either indoor or other. (2, page 34) Blackley explains there is no such thing as "common dust" as most dust contains "germs and other organic bodies found in the dust of any district will also depend upon the meteorological conditions which prevail in that district." He notes that dust produces hay fever symptoms mainly only during the hay fever season. He did observe that hay fever symptoms may occur when dust is stirred up, as when a horse and buggy runs down a dusty road. He attributes this to pollen mixed with the dust.
6. Pollen: Noted by many authors as the principle cause of hay fever symptoms, Blackly aims to prove this by a variety of experiments, most of which included applying a small amount of pollens from various trees, plants, weeds and grasses to the mucous membranes of the respiratory tract of himself or his colleagues. "Almost every experiment (with pollen) is by a greater or smaller amount of definite and unmistakable effect which seems to point to pollen as the most powerful if not the only cause of the malady." Pollen may also bring about hay asthma by reflex action. Blackley notes that four other physicians (Dr. Wyman, Dr. Kirkman, Dr. Marsh, and Dr. Patton) also did experiments on pollen, and all but one resulted in hay fever symptoms. He also notes that a high temperature causes a high rate of pollen. This sort of helps explain the older theory that heat caused hay fever. High heat with moisture will increase pollen production, and high heat with drought will slow pollen production. If the weather is warm and moist early in the season, pollen production may be early and end late, resulting in a shortened hay fever season. The mystery that remains is what is in pollen that induces hay fever symptoms. Another thing that may cause hay fever is animals. This may be due to the fact the animals are carriers of pollen.
7. Light and Heat: There is no evidence that shows light produces the symptoms of hay fever. That heat causes hay fever, as Dr. Bostock suggested in 1819, is also not very likely. If this were the case, hay fever would occur during the winter when rooms are heated to temperatures equal to a warm summer day. Although, experiment does confirm, as Bostock suggested, that cooler temperatures result in less hay fever symptoms, yet this is due to the production of less pollen, and not due to the temperature itself. Warm weather, as noted above, results in greater pollen production, and therefore it is not the heat that causes hay fever, but the increased pollen production. Likewise, if heat produced hay fever, the symptoms would not cease during a drought. Also of interest is some people escape to the White mountains to find relief due to the cooler temperatures. However, Blackley notes the temperatures are simlar in the White Mountains to the temperatures in the homes of many who vacation there as part of their annual hay fever holiday. Also, people in India claim to never have hay fever. If heat caused hay fever, people of India surely would have a greater incidence of it. It's also interesting to note some indicate hay fever symptoms are worse in the country than in the towns, yet the temperature is the same in both places. So there is basically no evidence that either light or heat produce hay fever symptoms. More likely, hay fever is less prevalent there because it is hot and dry. (8, pages 133-136)
8. Animals: Morill Wyman notes a variety of reasons why he suspects animals and insects to be a possible exciting cause of hay fever. For instance:
- (Insects may nourish on the plants during the catarrhal season
- Hemholtz found infusoria in his nose and found quinnine killed them, and quinnine is known to be an effective remedy for hay fever
- Dr. Charlton Bastian developed hay fever after dissecting a parasite of a horse.
- Emanations from some animals produce asthma in some persons
- One physician found caterpillar hairs to produce hay fever
- Cows, cats and dogs have a tendency to cause asthma in some persons
- Germs may be considered minute organisms and they cause disease
- Dried bacteria may blow in the wind
- Gaslight: proven false because such light is used during winter when it's not hay fever season
- Railway smoke
- Bad air
- Brimstone matches
- Animals (dogs, cats, horses, rabbits, guinea pigs, wild animals)
- Linseed meal
- Feathers (such as feather pillows and beds)
- Drugs (ipacacuanha, lycopodium and sulphur)
- Fresh coffee
- Wood from oak
- Food (tomatoes, watermelon, caterpillar)
To prove this, Blackly says he visited the sea-shore on a windy day without any symptoms of hay fever. An attack of hay fever occurred. At first he suspected that maybe the old theories of light or ozone were in fact true, because there appeared to be no other cause of his symptoms. But, upon further review, there he found a field where "wheat was in full bloom." He notes stories described by past authors on the subject of hay fever of how people on sail boats developed hay fever symptoms, and attributed it to heat. Blackley's experiments aimed to prove it was pollen in the wind, and not heat, that caused the symptoms.
So, knowing that hay fever symptoms would not occur without some sort of exciting cause, Blackly set out to do some research, and then to perform some experiments. Actually, at first theorized that there would be such scanty amounts of pollen in the air it would have little to know effect on hay fever sufferers. This was likewise the theory of Dr. Phoebus who stated: (2)
'It is a question whether we have to seek the exciting cause of the whole attack in those atmospheric conditions or in those matters which are found floating in the atmosphere, which we shall speak of as decided causes of aggravation. It is, however, scarcely probable that they, passing more or less quickly, contribute considerably to the creation of the attack—an attack which recurs periodically for life. The scantiness of the causes would, we should think, stand in a disproportion to the greatness of the effect.'By collecting samples of pollen from varoius locations, he proved that hay fever is less abundant in towns because there is less pollen in the air. It is more prevalent in the country because there is more pollen in the air. Of course, the amount of pollen in the air of a city will be relative to the surrounding area. (3)
Another thing that interested Blackley is how far pollen can travel. He notes that Darwin proved dust can travel quite a long ways so long as "strong winds have carried the dust into the upper atmosphere." Darwin said he found that dust can get up high in the stratosphere, and can land on boats in the middle of the seas.
He found that dust may be carried by wind from Africa to U.S. ships in the Atlantic.
Darwin also describes "buckfuls of pollen... have been shoveled off the decks of vessels near the North American Shore; and Mr. Riley has seen the ground near St. Louis in Missouri, covered with pollen, as though sprinkled with sulfur; and there is good reason to believe that this had been transported from the pine forests at least 400 miles to the south. Kerner has seen snow fields on the higher Alps similarly dusted." (4)
This also found to be true of volcanic ash, which was found when ash erupted from a volcano in Mexico was found to travel up to 750 miles. Blackley lists several examples of pollen traveling long distances and landing mysteriously in places you wouldn't expect to find much pollen, such as a "yellowish powder" falling "in the Windsor country. The yellow powder was studied and found to be pollen from a tree hundreds of miles away.However, Blackley notes, most of the time when pollen travels it is invisible to the naked eye, and may seem to cause sniffles and sneezes for no otherwise apparent reason. (4)
Based on this evidence, Blackley notes that: (7)
It is, however, certain that during the summer time this dust must be largely impregnated with pollen, and that whenever those who are susceptible to the action of this body come in contact with the dust so constituted it will give rise to the symptoms of hay-fever; but I need hardly point out that it is not the dust, but the pollen which it contains, which is the active agent. It is the want of a due appreciation, or the want of tbe knowledge of such facts as are given above, that has caused some authors to persist in regarding dust as one of the most potent causes of the malady.So, this lead to further studies and further experiments regarding pollen. Formerly, many physicians recommended travel to high altitudes to get away from hay fever symptoms. If this were true, Blackley suspected, then traveling up into mountains would prevent hay fever.
He did, however, suspect that high altitudes did prevent hay fever in many instances, as had already been proven. Although, he had observed on some occasions hay fever did occur even at higher altitudes, and, the reason he suspected, was due to showers of pollen that traveled long distances in the upper strata. Many physicians wondered, as did Blackley: do high altitudes benefit hay fever sufferers?
"This is, however," Blackley notes, "a question that can only be answered by actual experiment." He created a pollen trap that he connected to a kite and sent it high into the atmosphere. He had another pollen trap closer to the ground. He expects to find pollen up high, but not much. However, despite his prediction, he notes: (5)
"I found, however, in this instance, that the pollen in the upper strata was very largely in excess of that of the lower strata. The number of pollen grains obtained with the lower slide was ten. On the upper slide the number was one hundred and four. I was considerably surprised at this result, and felt sure the slides must have been changed in some accidental way after being taken out of the instruments to be examined under the microscope."The next two years he repeated the experiment, and obtained similar results. Of all the experiments he performed over several years, there was a quantity of pollen in the upper strata 19 times greater than the lower strata (or the strata of air that is found where people are, or pollen that is inhaled, and may cause hay fever). (6)
He used his evidence to answer other questions asked by physicians. Dr. Wyman, as well as Dr. Blackley himself, wondered why a pollinating plant in his sleeping room did not cause hay fever. Blackley said the answer must be because in a bedroom there is not sunlight or wind to create a breeze, and therefore the pollen drops from the plant to the floor. Thus, no the pollen will not be inhaled unless the plant is stirred. (7)
Basically, he proved that pollen wind causes pollen to make it's way into the air inhaled. Wind carries pollen to the upper strata where it follows the air, and becomes deposited as far away as a sail boat out at sea. And, thus, he proved that it was not heat that caused men to develop hay fever symptoms while sailing, but pollen. (6)
Of interesting to note is that during the course of his studies he observed that there were other germs in the air he studied along with pollen. He was curious as to whether these also may cause disease. He notes that "of the nature and origin of this latter I shall not at present offer an opinion." Although, he wonders: "Can atmospheric currents convey the active causes of disease from one continent to another?"
- Blackley, Charles Harrison, "Hay fever: it's causes, treatment, and effective prevention," 2nd edition, London, Bailliere, Tindall, and Cox, pages 69-142
- Blackley, ibid, page 144
- Blackley, ibid, page 169
- Blackly, ibid, page 172, 183, 184
- Blackley, ibid, page 176
- Blackly, ibid, page 178, 180
- Blackley, ibid, page 185-186
- Hollopeter, William Clarence, "Hay-fever and its successful treatment," 1898, Philadelphia, P. Blakiston's Son and Co.
- Wyman, Morill, "Summer Catarrh," 1876 (first edition was published in 1872), New York, Hurd and Houghton