This word is one which has come into use in relatively recent years and is used to name the state where one reacts to substances in a way differing from the average normal person. For example, there are some people whose lips thicken, eyes swell shut, and nasal passages narrow, or in whom asthmatic symptoms may appear very quickly after eating certain foods. It is not uncommon that the skin of some individuals breaks out in a kind of eruption when they come in contact with certain plants, such as the poison oak or poison ivy. We say those so affected are sensitive to these foods or plants. It is as if they were poisoned in contact.
Persons with these abnormal reactions have had some changes occur in their bodies in an unexplained manner, which result in the smooth or involuntary muscle tissue reacting in an unusual way to food or some other sub-stance. This condition is similar to that which was originally called anaphylaxis, but is now more generally called allergy. For the purpose of this discussion the word hypersensitiveness may be used as having essentially the same meaning.
If a very small amount of egg-white is injected into a guinea pig, in the course of a few weeks the cylinder of smooth muscle tissue lining the terminal air tubes in the lungs becomes highly sensitized to the egg protein.
If at this stage, egg-white is injected again, the sensitized smooth muscle tissue in the lungs contracts to such a degree that the guinea pig cannot breathe and dies from what was first called anaphylactic shock. We might call this an extremely severe experimental allergy of the food asthma type.
If a child has diphtheria, diphtheria antitoxin must al-ways be given as part of the treatment. This is made from horse serum. The injection of the horse serum often brings about a sensitiveness to the proteins of the serum. This sensitiveness will wear off in the course of time, but if while the child is sensitive to horse serum, he steps on a rusty nail necessitating the use of tetanus antitoxin, also made from horse serum, a severe and troublesome urticaria or skin rash may follow. This should not be interpreted as meaning that the tetanus antitoxin should not have been used. Before giving horse serum to a patient one must always inquire whether he has been given preparations containing it at any time, and if so how long before. This problem of giving antitoxin in the presence of hypersensitiveness was worked out during the World War. The soil of France was teeming everywhere with germs of lockjaw or tetanus. Each soldier with a dirty wound was given the proper dose of tetanus anti-toxin. Many of these soldiers were brought in unconscious so no questions could be asked. The army rule called for the giving subcutaneously of an initial injection of a very small amount of the serum to be used. If this injection produced a wheal, or raising of the skin, fifteen minutes later a similar amount was given. This was continued until the patient was sufficiently desensitized as evidenced by no reaction. When desensitization was attained the proper dose of protective serum was given.
Any normal person could probably be sensitized to a foreign substance, provided it were injected hypodermically. Numerous experiments have shown sensitiveness is often developed following the eating of certain foods, and the use of these foods is accompanied by reactions of varying degrees. Sensitiveness in babies at times is trace-able to the mother eating a food and passing the sensitiveness to her child during the nursing period.
In our food studies we are dealing not with artificially produced sensitization due to the injection of some foreign protein, but with a sensitization toward some constituent in food, often minute, which appears in the patient because of some peculiarity of his make-up. A large percentage of our population may be mildly or transiently sensitized to some substance. The feeding problem be-comes serious only when a patient is constantly sensitized to one or more foods. Fortunately, only a very small percentage of the population is habitually afflicted in this manner, at least to a degree that produces symptoms.
Some of the outstanding examples of allergy are: hives or urticaria in which the skin is sensitive to foods, drugs or other substances; angioneurotic edema which is characterized by large swellings on the surface of the bodysometimes the eyelids, lips, fingers, or feet may swell; food or drug eczema in which the skin is sensitive to foods or drugs; hay fever in which the numerous membranes lining the eyes, nose, and upper respiratory tract are sensitized to pollens; vasomotor rhinitis, better called allergic rhinitis, and sometimes called the “perennial cold,” in which the mucous membrane lining the nose is sensitive to foods and other substances; bacterial asthma in which the smooth muscle in the air tubes of the lungs is sensitized to bacterial proteins; food asthma in which this same tissue is sensitized to some food; allergic migraine, a condition in which the blood vessels of the brain are sensitized, sometimes to foods such as chocolate, and sometimes to the patient’s own internal secretions; intestinal allergy, in which the bowels or various parts of them are sensitized to foods or products of digestion; and joint allergy, in which the muscles in the blood vessel walls are sensitized to food or bacterial products.
The exact cause of this peculiar phenomenon is unknown. We do know that in the outstanding cases there is usually an hereditary background; the grandmother may have had bronchial asthma, the mother, hay fever, and the baby, food eczema. In 1902 Charles Richet created the term “anaphylaxis” in order to designate a curious tendency that certain poisons possess of increasing instead of diminishing the sensitivity of the organism to their action. Lesne and Dreyfus (1911) suggested that the fundamental error might be due to an insufficiency of digestive juices resulting in the absorption of incompletely-split proteins and a subsequent development of hypersensitiveness. If this is true it would explain food allergy, and it might also explain hay fever on the basis that the patient is unable to break up certain pollens which contaminate his food. Bacterial asthma could be explained by assuming that the proteins of bacteria or bacterial products have entered the body tissues by way of the digestive tract. Oelgoetz goes one step further, saying that normally, sufficient pancreatic juice is secreted to combine with all the food eaten and to provide an excess which passes free (uncombined) into the blood stream where it acts as a buffer solution, combining with and digesting any food which has been absorbed unmixed with enzymes. It is possible that hypersensitiveness to foods is caused by an excess of free food (free of enzymes) in the blood stream, and that this excess is caused by a deficiency of pancreatic secretion. Our own studies of digestive functions and the results obtained when especial attention is paid to improving them in various ways, would seem to support these theories. It should be stated, however, that the actual demonstration of food as the cause of allergy can be made in relatively only a small proportion of hypersensitive persons.