1898: Dr. Hollopeter: What Causes Asthma?

According to William Hollopeter in his 1898 book "Hay-fever and its successful treatment, there were essentially two causes of hay fever: (1, page 47)

1. An exciting cause (heat, pollen, dust, sunlight, etc.)
2. A preexisting, underlying condition 

Provided statistics of the era, Hollopeter said that relatively few people have hay fever, which verifies that some "underlying condition, predisposition, or idiosyncrasy can hardly be doubted. Exactly what this is, or on what it depends, is unknown." (1, page 47)

Holopeter said that the first person to talk about a predisposition to developing hay fever was Dr. Abbots Smith in 1865.  Likewise, Holopeter said: (1, page 47)

This predisposition or idiosyncrasy has generally suddenly developed without apparent reason. It has been argued that it is systematic or central, and that it is due to some local abnormality of the mucous membrane, the capillaries, or the periphery of nerves. Once acquired, however, it is seldom lost, and it apparently increases with each successive year.

The following are the major predisposing factors:

1. Race: English and Americans are the most susceptible.  One physician went as far to suspect that sine Americans and English were the most likely to drink tea, that perhaps tea somehow affected the nervous system causing hay fever. Although the Chinese and Japanese drink tea as well, and there's a low incidence of the disease in those nations. 
2. Geographic distribution:  It is rarely found in northern regions, such as Canada, Norway, Sweden and Denmark.  It is most commonly seen in the U.S., Europe, and to some degree New Zealand and Australia. Even in the U.S. and England is is not commonly found along the seashore and at high elevations.  It is difficult to know exactly where it's most likely to occur. (Dr. Wyman published maps for where it's most likely to occur in his 1872 book "Autumnal Catarrh." (1, pages 49-52
3. Heredity:  George Beard was the first to postulate a nervous origin of hay fever, and that it was acquired through inheritance. Various physicians have shown evidence of the malady among the various generations of the family tree (Morill Wyman, F.H. Bosworth, Morell Mackenzie) (1, page 53)  
4. Sex:  Generally, "of the 433 cases cited by Phoebus, Wyman and Beard, only 143, about one-third, were females." So the tendency is that it affects males more so than females.  Morell Mackenzie also noted the trend, noting he had 38 male patients with hay fever, and only 23 females. The theory is that "men are more exposed to the exciting causes such as dust, heat, pollen, etc., although females are more neurotic."(1, page 54)(2, page 96-7)
5. Age: While occasionally occurring in people over the age of 60, it generally first appears in people under the age of 40. (1, page 55)  In many cases of childhood onset hay fever, many cases are regarded as the common cold, unless the parents were also afflicted with it (hence suggesting the hereditary component). 
6. Education: Holopeter notes pretty much the same as every other author on the subject, that: "Most all writers on this subject have observed that the disease attacks the better educated classes and those of fair social position. It is rarely met with among the laboring classes. This would seem to emphasize the view that the disease is essentially a neurosis. From the notes of sixty-one cases of hay-fever in private practice, and the sight of many others of which no record was kept, Morell Mackenzie found all the patients persons of some education, and recalled having seen none among his hospital patients. Of fortyeight cases of Blackley, all were educated, and Wyman made the same observation. Edmund W. Holmes has shown that the ignorant classes are not so likely to recognize the disease as a distinct affection, and apply for medical aid." (1, page 55)(3, page 204)
7. Occupation and Mode of life: The "rustic" and farmers are much more exposed to exciting causes and therefore are less susceptible to developing hay fever. Others suggest it only effects the wealthy because they have a higher intelligence.  (1, page 56)  Wyman observed, among the occupations he observed, those most likely to have hay fever have "indoor jobs requiring but little manual labor," such as merchants and manufacturers. Wyman notes that only three farmers in his little study had hay fever, and this was of interest to him.  He surmised that they probably did have hay fever, "  (2, page 99-100) 

Of this observation regarding the low number of farmers with hay fever and the high number of merchants and manufacturers, Wyman writes the following: (2, page 100)

"It is not a little remarkable that of those who must make up the largest class in the community, so few should be reported as subjects. It may be that the disease with them is light, and therefore overlooked entirely, or not thought of sufficient importance to apply for medical aid. This, to a certain degree, is not improbable, for we find that physicians to whom application is made, do not all recognize it sufficiently to ask whether the disease has recurred annually, nor do the patients think it worth mentioning, even if it has been observed and remembered. It is by no- means infrequent for a person to experience several pretty severe annual attacks before it occurs to him that probably these are returns of one and the same disease. Still, the mechanics and farmers of New England are too intelligent and too well educated to allow the disease to escape their observation entirely. If many applied for treatment at the dispensaries of the large cities, the fact would appear in their annual reports. No such disease is mentioned.

I am inclined to think, therefore, that the disease is less severe or less frequent with those that labor, than with those whose employments are attended with less muscular exertion. The result, perhaps, of a life more in accordance with the rules of health, in this respect, for the mechanics and farmers of New England, as a general rule, are as well housed, clothed, and fed, so far as health is concerned, as those who are among the richer and in some respects more favored classes. This question, however, can only be satisfactorily settled when a knowledge of the disease becomes more general."

The following are theories as to what might cause hay fever:

1.  Pollen Theory:  It is the most generally recognized as the cause of hay fever, and while it was a speculated cause prior to the 1860s, experiments by Dr. Charles Blackley proved it during experiments he performed between 1866 and 1878.  He proved that contact with pollen to the mucus membrane causes inflammation and redness, and hay fever symptoms. He wrote that there is a direct relationship between the amount of pollen in the air and hay fever symptoms. For more on Blackley's pollen theory of hay fever you can click here. 

2.  The Neurotic Theory: Holopeter basically refers to George Beard, who in 1876 postulated the nervous  theory of hay fever, and made light to allay the "misconception" that nervous meant "debility and emaciation." Holopeter notes that Beard explains the truth to be more along the lines that the nervous system is full of full of "great strength and endurane." In those with hay fever, some exciting cause "excites" the nervous system to cause the symptoms of hay fever.  Beard explains that the the disease and the tendency to be transferred from one generation to another was all based on this nervous theory.  No evidence has yet been shown of how the nervous system causes the hay fever symptoms. (You can read more about Beard's Nervous Theory of Hay Fever by clicking here)(1, page 57-60) 

• Vasomotor susceptibility:  Vasomotor refers to the nervous systems ability to regulate dilation and contraction of blood vessels.  In hay fever it has a tendency to cause dilation of the blood vessels lining the respiratory tract and eyes, hence hyperaemia and inflammation (catarrh) and your hay fever symptoms. That this happens "indicates a neurotic tendency." Some suspect it may or may not be due to lesions. A similar event occurs with asthma, only the dilation and hyperaemia occurs in among the air passages of the lungs.  (Hyperaemia refers to increased blood flow to a certain region of the body) Hollopeter notes that "Bosworth is inclined to think a peculiar lack of vasomotor control characterizes the neurotic manifestations." (1, page 57-60)
• Idiosyncracy:  The fact hay fever has idiosyncratic means it's neurotic.  By this, the body of the hay fever sufferer is oversensitive to some exciting cause. 

3.  Local Disease Theory: Some sort of local disease (polyp, deviated septum, rhinitis, obstructed nasal passages, etc.) may be the cause of the disease. When the polyp is removed, the hay fever may be cured. Hollopeter quotes Mackenzie:  "there exists in the nose a well-defined sensitive area whose stimulation through a local pathologic process, or through an extra irritation, is capable of producing an excitation which finds its expression in a reflex act or in a series of reflected phenomena."  Bosworth suggested these were generally the effect rather than the cause of hay fever. Some physicians propose such local agents cause both hay fever and asthma. (1, page 62-64)

4.  The Uric Acid Theory:   In 1893, Dr. Seth S. Bishop, as quoted by Hollopeter, wrote: "an excess of uric acid in the blood causes hay fever, or nervous catarrh."  Hollopeter notes that excess uric acid in the blood "causes certain disturbances of a vascular and neurotic character. Haig wrote that excess uric acid causes contraction of arterioles and capillaries, and this opinion was verified by Thomas J. Mays. Murchison, Conklin, Ebstein, Quinquad, and others. Bishop in 1894 speculated that regulation of uric acid should be regarded as a treatment for hay fever. Mays believed that while uric acid was the cause, hay fever was still nervous and, therefore, still hereditary. Although Dr. Capp suggests that the presence of excess uric acid may actually cause "a central nervous irritation." This results in "nerve currents" that are uncontrolled by the normal functions of the body, and result in the abnormal response of hay fever.  (1, pages 64-71)

References:

1. Hollopeter, William Clarence, "Hay-fever and its successful treatment," 1898, Philadelphia, P. Blakiston's Son and Co.
2. Wyman, Morill, "Summer Catarrh," 1876 (first edition was published in 1872), New York, Hurd and Houghton
3. Holmes,