Geraniums, roses, heliotropes, and other sweet-scented flowers often bring on attacks. The bean in bloom and elderflowers are also regarded as causes.
Ragweed, also known as Roman wormwood, Ambrosia artemisiæfolia, a weed which extends almost over the whole of the United States, is a powerful cause of the autumnal variety, but, like all the other agents which have been accused of causing hay fever, is by no means general in its action, many patients being able to inhale the dust shaken from the flowers with perfect impunity even during the critical period. On those susceptible to its influence it will act not only during the hay-fever season, but also at other periods of the year. Wishing to study the plant, I procured during the fall several specimens of it and placed them between the leaves of a large quarto volume. During the winter my wife, who is a sufferer with hay fever, accidentally opened the book, and, seeing the plant, not knowing its nature, picked it up and smelt it. She immediately began to sneeze, the eyes and nose itched intensely, there was profuse lachrymation; in short, all the symptoms of a mild attack of hay fever supervened, the effects of which lasted until the following morning. The case is interesting from the fact that in this instance the experiment was made unconsciously, and the effects could not therefore be attributed to the imagination, the patient being entirely ignorant of the nature of the plant. The prevalence of autumnal hay fever appears to coincide with the blooming of the ragweed, and conforms to the geographical distribution of that plant, which grows wherever the disease prevails, while in exempted localities it is seldom found or never seen. In Bethlehem, N.H., a diligent search was made for it for two days by a botanical friend without his finding a single specimen, although in the neighboring town of Littleton, which is within sight of Bethlehem and is not exempt, the plant is quite abundant. Marsh states that he saw none of it in New Brunswick nor at Moosehead Lake.
Dust of various kinds is more frequently designated by invalids themselves as the cause of their disease than any other agent. Thus, in reply to his question as to the cause of hay fever, Beard received 104 replies assigning dust as the cause, while 540 attributed it to thirty other agents. All kinds of dust, both in and out of doors, are accused, but that of railway-cars is supposed to be the most potent.
There is but one case on record in which animal parasites were the cause of an attack—that of Bastian, who while engaged in the spring investigating the anatomy of the Ascaris megalocephala, one of the parasites of the horse, noted that its emanations not only in the fresh state, but after having been kept in spirits for two years, invariably caused itching about the eyelids, irritation of the conjunctivæ, with continuous sneezing and other symptoms resembling hay fever. These symptoms ceased after two months, and did not return until the following spring. He finally became so sensitive that the wearing of the coat in which he had worked during the examinations was sufficient to bring on the symptoms.13
13 Salisbury in Infusorial Catarrh and Asthma attributes hay asthma to an animalcular organism, the asthmatos, but his assertions have not as yet been confirmed by other investigators.
Helmholtz, himself a sufferer from hay fever, discovered that the secretion of his nasal mucous membrane contained during the attack a number of vibriones, and, never being able to find them there at other times of the year, concluded that they were the cause of the disease. Binz of Bonn having discovered that quinine was inimical to the vibriones, Helmholtz supposed that that agent would be the proper one to employ in the treatment. He used it with success, injecting a saturated solution into the nostrils, the injection each time affording marked relief.
THE POLLEN THEORY.—Believing from his own experience and that of others that hay fever was due to the pollen of certain plants, Blackley of Manchester instituted a series of ingenious and instructive experiments to prove the correctness of his conclusions. In his first set of experiments a very small quantity of the pollen of various plants was applied to the lining membrane of the nostril. That of the Lolium italicum produced at first a slight feeling of anæsthesia at the point to which the pollen had been applied, followed "by a feeling of heat which gradually diffused itself over the whole cavity of the nostril and was accompanied by a slight itching of the part. After some three or four minutes a discharge of serum came on and continued at intervals for a couple of hours." The mucous membrane became so swollen as to partially occlude the nostrils and impede the entrance of air. When rye was used the symptoms were much more violent, and were attended by violent and long-continued fits of sneezing. With wheat and oats the effect was equally decided. The same experiment was tried with other orders of plants with varied success, some of them being very active, while others were found to be quite inert. One grain of the pollen of Alopecarus pratensis was applied to the fauces, causing itching and diffused redness. That of the Lolium italicum rubbed into the abraded skin of the forearm, as in vaccination, produced itching and swelling.
Marsh,14 who has repeated Blackley's experiments in America, gives some very interesting facts in regard to the pollen of the Ambrosia artemisiæfolia. On the 5th of August, 1874, he placed a few sprigs of the ambrosia in full bud, but without open flowers, in a glass of water in his office. The next day the flowers were open, and on handling the plant for the purpose of preparing some microscopic specimens from it, the pollen was freely scattered around. This caused in him severe coryza of twenty-four hours' duration, with occlusion of the nostrils and serous discharge. On August 13th he repeated the experiment, this time intentionally applying some of the pollen to the nostrils. This produced such severe symptoms that he had to have recourse to a hypodermic injection of morphia for their relief. These, however, continued into his regular attack, which should have been due a few days later.
14 Op. cit., p. 14.
Having proved that the pollen of certain plants was capable of producing hay asthma, Blackley next turned his attention to the determination of the amount of that substance floating in the atmosphere of different places and at various periods of the year. The plan which he found best adapted to his purpose was to expose slips of glass to the open air for a given length of time, so as to allow any solid matter the air might contain to deposit upon the glass. On each of these slips a space of one centimeter square was made sticky by covering it with a mixture of water, proof spirit, and glycerin. These were exposed to the atmosphere for twenty-four hours, and then placed under the microscope and the number of pollen-grains adhering to the moistened square counted. These slides were exposed at the height of four feet nine inches above the ground, "the average breathing-level," and were placed in a grass meadow four miles south-west of Manchester. The experiment was begun early in April, 1866, and continued until the 1st of August. Only a small quantity of pollen was found during the first month. On May 30th it appeared in much larger quantities, and continued to appear on most of the days until August 1st. Barometric pressure did not influence the deposit of pollen, but whenever the air was drier the quantity was increased. A fall of rain, especially if attended with lowering of temperature, had the effect of materially lessening the number of grains. The largest quantity of pollen was obtained on June 28th, the day after the highest temperature of the season, showing that a large deposit of pollen coincides with, or follows, a marked rise in temperature. Fully 95 per cent. of the pollen collected belonged to the Graminaceæ, but this would not apply to other localities and countries, in which that of other plants would naturally predominate. These experiments were quite successful in demonstrating that the rise and progress of the disease corresponded with the amount of pollen present in the atmosphere. A third set of experiments was made by attaching the glass slides to kites, to determine the amount of pollen present in the air at different altitudes. These experiments revealed the fact that grass pollen was much more abundant at elevations of 500 to 1500 feet than near the surface of the ground. Marsh also investigated this portion of the subject, only, instead of attaching the slides to kites, they were placed in the attic windows: he arrived at conclusions in regard to the pollen of ambrosia similar to those which Blackley had reached with reference to the Graminaceæ.