8 George M. Beard, M.D., Hay Fever and Summer Catarrh, New York, 1876.
9 "Hay Fever or Pollen-Poisoning," an essay read before the New Jersey State Medical Society by Elias Marsh, M.D., Paterson, N.J., 1877.
ETIOLOGY.—In scarcely any other disease is there such a diversity of opinion in regard to the cause as in hay asthma. We have seen how Bostock and his contemporaries differed on this point, he attributing it to heat, while of the others one claimed that it was caused by the air of hot-houses and green-houses, and another insisted that it was neither of these, but the flowers of certain grasses. Since that period other theories of causation have been advanced, but the same diversity of opinion as to its origin which marked its early history continues even at the present day.
In treating of the etiology of hay fever the various causes may be divided into two classes—viz.:
Predisposing Causes.—The fact that hay asthma is frequently transmitted from one generation to another, so well established by Wyman, is now very generally admitted, and will become more apparent in the future, as in estimating this feature it must be remembered that we have to deal with an affection which seventy years ago was entirely unknown and which has only recently become generally recognized. That the fact of the hereditary transmission of the predisposition is becoming every year more generally accepted is made apparent by the replies to two sets of circulars addressed to hay-fever patients in different years. Thus, Wyman, whose circular was issued at least eight years ago, received 18 affirmative replies out of 80, a little less than 25 per cent.; while to the writer's circular, issued in 1882, there are 25 affirmative replies out of 66. Numerous instances have been recorded where the disease attacked not only two, but even three, generations of the same family.
Hay asthma appears to be much more prevalent among males than females, the proportion being 3 males to 2 females. There is no apparent reason for this discrepancy other than that males are as a rule more exposed to the vicissitudes of weather, and that the restless energy with which many of them carry on their avocations predisposes to the disease.
The causes which produce hay fever act alike upon many thousands, an infinitesimal percentage of whom are attacked. There must therefore be some individual peculiarity which predisposes certain persons to the affection, but, aside from the facts that those attacked are usually of a nervous temperament, and that the respiratory mucous membrane of many of them is extremely sensitive, and that the vascular erectile tissue over the turbinated bones and lower portion of the septum is often hypertrophied,10 there are no known peculiarities by which it can be recognized. What races are subject is a question which thus far has received but little attention. To the writer's knowledge, the only well-established fact relative to race susceptibility is that negroes are exempt from the disease, and that in India (Blackley) it does not occur among the natives.
10 Roe, The Pathology and Radical Cure of Hay Fever, 1883, p. 9.
Statistics show that it is much more common in youth and middle age, and that comparatively few are attacked after forty, as will be seen by referring to the following table:
| Age when First Attacked. | Wyman's Cases. | My Own Cases. | Total. |
| Under 10 10 to 20 20 to 30 30 to 40 40 to 50 After 50 | 11 11 25 8 11 2 | 10 17 13 11 5 1 | 21 28 38 19 16 3 |